Wave energy apparatus having a venturi shroud

ABSTRACT

By optimizing the degree to which water is accelerated through a venturi device, the amount of power that an energy device extracts from the ocean is maximized. Prior venturi-based wave energy devices have proven to be inefficient because of the relatively small amount of power that they generate relative to their size and cost. By optimizing the venturi effect created within the submerged venturi components of such devices, the speed of the water moving through the narrowest portions of such a devices is maximized with respect to the wave environments in which they operate, and a maximal amount of energy is extracted from the ocean. This optimization of a wave energy device&#39;s power is sufficient to render such devices cost effective. The method of extracting energy from the accelerated flow of water moving through such venturi devices is not limited, and many alternatives exist, each with its own potential benefits.

RELATED APPLICATIONS Cross-Reference to Related Applications

This application is a divisional of U.S. patent application Ser. No.12/777,409, filed May 11, 2010, (whose entire contents are herebyincorporated by reference) and which is a continuation-in-part of U.S.patent application Ser. No. 12/389,928, filed Feb. 20, 2009 (whoseentire contents are hereby incorporated by reference) and the Ser. No.12/777,409 application also claims the benefit of the prior filing dateof provisional patent application Ser. No. 61/278,327 filed Oct. 5,2009, entitled “Venturi, Chambered Venturi and Optimized Venturi-BasedOcean Wave Energy Device” and incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates, generally, to wave-driven energy conversiondevices that convert the abundant natural energy present in the oceansand other bodies of water into electrical or chemical energy.

2. Description of Prior Art

2a. Overview

2a1. Water Turbines

Water turbines have been used to extract useful energy from movingwater, or water under pressure, for thousands of years. Many differenttypes of water turbines have been invented and used in the past toextract energy from water under a variety of circumstances, e.g.,Francis turbines, Pelton turbines, Kaplan turbines, etc.

The design of water turbines is a mature discipline. Most modern waterturbines convert the kinetic and/or potential energies of water intorotary motion that can be used to create electricity. The efficienciesof these mature turbine technologies can be quite high, often exceeding90%. And it is relatively easy to find an existing water turbine designthat will optimally harvest the kinetic and/or potential energyavailable in almost any river or dam.

2a2. Wave Energy Devices

Attempts to extract energy from waves moving across the surface of anocean are relatively new. Some devices of this type have been built,described in prior patents and proposed in the literature.

There are many good reasons to engage in such research and developmentefforts. Ocean waves represent a renewable energy source whoseharvesting would not degrade the environment and ecology of the earth.Ocean waves also represent a very concentrated energy source, offeringthe potential for the harvesting of large amounts of energy usingrelatively small devices.

Most wave energy devices are constrained to use in relatively shallowocean waters where they may be anchored in some manner to the oceanfloor. When anchored to the ocean floor, a wave energy device may createand exploit a tension between the immovable ocean bed and the verticaloscillations of the waves. These types of devices are generally notcapable of operating in the deeper parts of the ocean.

Among the many wave energy devices proposed or built, some are able tooperate in the deeper parts of the ocean. Many of these devices utilizea buoy at the surface of the ocean, and a submerged component, which, inone way or another, exploits the relatively motionless waters which arefound a short distance below the ocean's surface to facilitate theextraction of energy. Some of these devices utilize submerged turbinesthat are moved through the still waters by the action of waves abovecausing the turbines to rotate and generate power.

2a3. Energy in Waves

Waves traversing the surface of the ocean represent a repository of alarge fraction of the total energy imparted to the earth by the sun. Thesun heats the land and the oceans and much of this heat energy passesinto the atmosphere. Differential heating of the atmosphere across thesurface of the earth, in conjunction with the rotation of the earth,causes the atmosphere to move across the Earth's surface, sometimes atrelatively high speeds.

When the atmosphere moves over the surface of the earth's lakes andoceans, it imparts some of its kinetic energy to the waters at thesurfaces of those lakes and oceans, thereby creating waves on thesurfaces of such bodies of water. The amplitudes of those waves increaseas long as the wind blows parallel to the direction in which the wavesare propagating. The uninterrupted distance over which the wind blows ina direction parallel to a wave's propagation, and over which it impartsincreasing amounts of energy to that wave, is called the “fetch” of thewave.

Typical ocean waves range in height from three-tenths of a meter (0.3 m)to five meters (5.0 in). At higher (i.e. more polar) latitudes,ten-meter (10.0 m) waves are not uncommon.

2a4. The “Wave Base”

Water molecules and other particles contributing to the propagation of“deep-water” waves (i.e. those moving across waters with depths of about50 feet or more) have circular orbits. (These orbits become ellipticalas the water becomes shallower.) In deep-water waves, the radii of theorbits of the water molecules decrease exponentially with increasingdepth. The radii become vanishingly small as the depth approachesone-half the wavelength of the waves. This special depth is called the“wave base.” A wave in the ocean does not move the water located belowthe wave base to any significant degree. The water below this depth andany objects floating in it are substantially stationary, even as wavesmove across the surface overhead.

It is possible to use the motion of waves at the surface of the ocean tomove a submerged component up-and-down through the relatively stillwaters beneath the waves, e.g. beneath the wave base.

2a5. Extracting Power From the “Still” Water Beneath the Waves

The prior art includes a type of wave-energy device capable ofextracting power by leveraging the motion of waves at the surface of theocean against the still waters located beneath the waves UK Patent45018/72 by J. Bichard, 1973. See FIG. 1. It includes a unidirectionalor bi-directional propeller suspended from a buoy by a shaft or cable.As the buoy moves up and down in response to passing waves, thepropeller is moved up and down through the relatively still waters belowthe surface. This up-and-down motion of the propeller through relativelystill waters compels the propeller to spin. The propeller spins in aconstant direction if the propeller is bi-directional but its directionof rotation reverses if the propeller is unidirectional. Such a devicedoes not generate much power.

Even though the force driving the water back and forth through such asuspended turbine would be great, the speed of the water's movementthough the turbine would be relatively slow. When driven by waves with aheight of 4 meters and a period of 8 seconds, the maximum speed of asuspended turbine relative to the water around it would be about 1.6meters per second. At this speed, it would be difficult to extract asignificant amount of energy from the flowing water with a simpleturbine because the amount of power that can be extracted from a flowingstream of water by a turbine is proportional to the cube of its speed.In other words,

Power available for extraction=0.5 A v³

Power actually extracted=0.5 k A v³

Where “A” is the cross-sectional area of the stream of water from whichpower is extracted (in this case, the cross-sectional area swept by therotating blades of the turbine), “v” is the speed of the water movingthrough the turbine, and “k” is a constant that equals the efficiency ofthe turbine.

A reasonably sized device of the kind illustrated in FIG. 1 (e.g. aturbine diameter of 7 meters), with a turbine of reasonable efficiency(e.g. k=0.5), would only produce an average of about 16 kW when drivenby waves with a height of 4 meters and a period of 8 seconds.

Since ocean waves rise and fall with a relatively slow speed (themaximum of which is generally only one or two meters per second), it isdifficult to extract much energy from the water constrained to flowthrough a propeller at that same slow speed.

2b. Device Proposed by Heck

In “Wave Responsive Generator” (U.S. Pat. No. 4,447,740) Heck claimed awave energy device that also suspended a turbine beneath a buoy like theone discussed above. However, Heck proposed surrounding his device'ssubmerged turbine with a cylindrical housing designed to shield theturbine from damage from under-water debris. Heck further proposed(although he did not claim) a modification to his wave energy device inwhich frusto-conical sections would be added to the ends of thesubmerged cylindrical turbine housing. The effect of thesefrusto-conical sections would be to accelerate the speed of the waterwhich entered the cylindrical turbine housing and which passed through,and powered, the enclosed turbine. Although Heck did not provide anyspecifics about the implementation of this modification, hisillustrations provide some information.

According to the drawings, e.g. FIG. 1 of U.S. Pat. No. 4,447,740, whichis duplicated in FIG. 2 of this patent, the frusto-conical extensions onthe ends of the cylinder in Heck's device (D_(t)=1.16 D_(h)) would berather small, and would be expected to increase the speed of the waterpassing through the associated turbine by 1.3× (a 30% increase) and toincrease the power generated by the associated turbine by 1.8× (an 80%increase). (See Section 2c below.)

2c. Heck Device Water Speed and Power

Refer to FIG. 2.

Dt=diameter of the opening of frusto-conical section appended to thecylindrical turbine housing, i.e. the diameter of the mouth of the Heckdevice.

Dh=diameter of the cylindrical turbine housing, i.e., the diameter ofthe throat of the Heck device, and of the turbine enclosed therein.

At=cross-sectional area of the mouth of the Heck device.

Ah=cross-sectional area of the throat of the Heck device, and of thewater flowing the enclosed turbine.

Vt=speed of the water entering the mouth of the Heck device.

Vh=speed of the water flowing through the Heck device, and through theenclosed turbine.

Pt=power available for extraction from the water entering the mouth ofthe Heck device.

Ph=power available for extraction from the water flowing through thethroat of the Heck device.

k=efficiency with which the turbine of the Heck device extracts powerfrom flowing water.

p=density of ocean water (i.e. 1025 kg/m3)

Pixel measurements of an image of FIG. 1 of Heck's U.S. Pat. No.4,447,740, which shows the embodiment of his device that incorporatesthe frusto-conical sections, yield the following relative measurements:Dt=304 pixelsDh=262 pixelsD _(h)=(262/304)D _(t)D _(h)=0.862 D _(t)Assume D_(t)=1.0 [a relative point of reference], therefore:D _(h)=0.862A _(t) =ΠD _(t) ²/4=Π/4=0.25 ΠA _(h) =ΠD _(h) ²/4=Π0.862²/=0.186 ΠV _(h)=(A _(t) /A _(h))V _(t)=(0.25 Π/0.186Π)V _(t)=1.3 V _(t)

The speed of the water passing through the turbine of Heck's wave energydevice would be expected to increase by a factor of 1.3, or by 30%, as aresult of the frusto-conical extensions appended to both ends of thecylindrical turbine housing, as illustrated in Heck's drawings.P _(t) =k 0.5 ρA _(t) V _(t) ³ =k0.5ρ(0.25Π)V _(t) ³=0.125 k ρV _(t) ³P _(h) =k 0.5 ρA _(h) V _(h) ³ =k0.5ρ(0.186Π)(1.3 V _(t) ³)=0.204 k ρΠV_(t) ³P _(h) /P _(t)=(0.204 k ρΠV _(t) ³)/0.125 k ρΠV _(t) ³)=1.8

The 30% increase in the speed of the water passing through Heck'sturbine would be expected to result in an 80% increase in the poweravailable for extraction, and in the power which would ultimately beextracted.

In keeping with the example offered in section 2a5 (paragraphs00019-00024), a reasonably sized Heck device of the kind illustrated inFIG. 2 (e.g. a venturi mouth with a diameter of 7 meters), with aturbine of reasonable efficiency (e.g. k=0.5) would produce an averageof about 30 kW when driven by waves with a height of 4 meters and aperiod of 8 seconds (an 80% increase over the earlier power level of 16kW—produced in the absence of any venturi device). However, the cost ofconstructing and maintaining a 7-meter diameter buoy and venturi device,including a 6-meter turbine, is unacceptably high for a device with anoutput of only 30 kW in rather energetic 4-meter oceans.

2d. Problems with the Heck device

The Heck device fails to generate enough power to justify its cost ofconstruction, deployment and maintenance.

Another problem with the Heck device is its use of a single central pipewhich encloses the turbine shaft and is also responsible for maintainingthe attachment, and fixing the position (in a rigid manner), of theturbine and the cylindrical housing. The stress on this single centralsupport would be much greater than necessary and introduce seriousconcerns regarding the ability of the device to survive the rigors ofits time at sea.

Therefore a need exists for an apparatus which is capable of utilizingthe energy of ocean waves to generate electrical energy which has thecapability of accelerating the water flowing through a submergedcomponent of the power generation system to the degree that sufficientpower is generated to justify cost of construction, deployment andmaintenance of the device and at the same time the device issufficiently robust to withstand the stresses imparted thereto by thewave motion at the surface of the ocean.

SUMMARY OF INVENTION

This invention provides an improved design for wave energy devices ofthe types proposed by Bichard and Heck, as well as an improved designfor all other varieties of venturi-based wave energy devices. Inaddition, this invention provides a method for optimizing the design ofthe venturi component used in these types of devices. This optimizationis made with respect to the degree to which the design's resultingventuri effect will accelerate the water flowing through the submergedcomponent of the power-generation system, e.g. a turbine or suctiondevice.

The preferred embodiment of this invention utilizes a venturi tubeembedded within an outer cylindrical housing. The preferred embodimentof this invention rigidly connects the submerged venturi tube to thebuoy above through multiple struts arranged about the periphery of thetube and the buoy. The preferred-embodiment of this inventionincorporates a venturi throat whose cross-sectional area is specificallydesigned to optimize the amount of power extracted from a portion ofocean perturbed by waves with specific patterns of wave height.

This invention is an apparatus for generating electrical energy whichincludes a flotation member which is to be disposed adjacent to theocean surface with a venturi having a mouth and throat disposed in theocean beneath the flotation device by means connected therebetween sothat the venturi moves responsive to wave action, the cross sectionalarea of the throat of the venturi relative to the cross sectional of thearea of the mouth of the venturi causes water flowing through the throatof the venturi to have a speed of more than two times the speed of thewater at the mouth of the venturi but no more than the choke speed ofthe venturi. A motion-generated means is disposed in the throat of theventuri and is connected to an electrical generator for producingelectrical energy.

This invention also includes a method for optimizing a venturi devicehaving a mouth and throat for generating electrical energy from oceanwaves which includes selecting the height of the ocean waves, selectingthe periodicity of the ocean waves, selecting the choke speed for thewater flowing through the venturi device and establishing the relativecross-sectional area of the throat of the venturi device as compared tothe cross-sectional area of the mouth of the venturi device so thatspeed of the ocean water flowing through the throat is at least twotimes the speed of the water at the mouth but no more than the chokespeed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a prior art turbine device;

FIG. 2 is an illustration of an additional prior art turbine device;

FIG. 3A is a cross-sectional view of a structure similar to that of FIG.2 but having a venturi designed in accordance with the principles of thepresent invention;

FIG. 3B is a side elevational view of alternative structure similar tothat of FIGS. 3A, but with a housing there about;

FIG. 3C is a partial cross-sectional side view of the structure as shownin FIG. 3B;

FIG. 4A is a side elevational view of a preferred embodiment of anapparatus constructed in accordance with the present invention;

FIG. 4B is a partial cross-sectional view of the device as shown in FIG.4A;

FIG. 5 is a partial cross-sectional view illustrating a turbine disposedat the throat of a venturi device;

FIG. 6 is a graph illustrating the effect of reducing the throatdiameter relative to the diameter of the mouth of a venturi device onthe relative throat area, relative water speed, relative availablepower, and relative device power;

FIG. 7 is a graph illustrating the choke speed of a venturi devicerelative to the depth of the device as disposed in the ocean;

FIG. 8 is a graph which shows the optimal available power which can bemade available for extraction within a venturi device through theselection of an optimal relative venturi throat cross-sectional area(expressed in the graph as the diameter of an equivalent circular area)with respect to a range of likely choke speeds with respect to aspecific wave height and wave period;

FIG. 9 is a graph which shows the optimal amount of power which can bemade available for extraction within a venturi device through theselection of an optimal relative venturi throat cross-sectional area(expressed in the graph as the diameter of an equivalent circular area)with respect to a range of likely wave heights with respect to aspecific choke speed and wave period;

FIG. 10 is a graph which shows the optimal amount of power which can bemade available for extraction within a venturi device through theselection of an optimal relative venturi throat cross-sectional area(expressed in the graph as the diameter of an equivalent circular area)with respect to a range of likely wave periods with respect to aspecific choke speed and wave height;

FIG. 11 is a graph illustrating the relationship of the power availablewithin a venturi device with respect to a range of possible relativeventuri throat diameters with respect to a specific wave height and waveperiod and choke speed;

FIG. 12 is a graph similar to the one in FIG. 11 but with respect to adifferent wave height, period and choke speed;

FIGS. 13A-13D are graphs illustrating the speed of the water at variousportions along a wave as depicted in FIG. 13A as well as the waterflowing through the throat of a venturi device as shown in FIG. 13C andthe power available in the throat of the venturi device as shown in FIG.13D;

FIG. 14 illustrates the actual speeds and relative power levels of aventuri device operating in water having a specific wave height, waveperiod and choke speed with respect to the device's relative throatcross-sectional area (expressed in the graph as the diameter of anequivalent circular area);

FIG. 15 is a graph illustrating power optimization curves similar tothat shown in FIG. 14, but with respect to different wave heights andperiods with a choke speed that is specific;

FIG. 16 is a graph illustrating the optimization of the relative venturithroat cross-sectional area (expressed in the graph as the diameter ofan equivalent circular area) with respect to different sets of expectedwave conditions;

FIG. 17 is a graph illustrating the optimization of the relative venturithroat cross-sectional area (expressed in the graph as the diameter ofan equivalent circular area) with respect to a combination of expectedseasonal wave conditions;

FIG. 18 is a table comparing the prior art device of FIG. 2 to anequivalent device optimized according to the principles of the presentinvention;

FIG. 19 is a graph illustrating the amount of power available forextraction from the prior art device as shown in FIG. 2 and by anequivalent device optimized according to the principles of the presentinvention;

FIG. 20 illustrates an alternative embodiment of venturi deviceconstructed in accordance with the principles of the present invention;

FIGS. 21A and 21B illustrate yet another alternative device constructedin accordance with the principles of the present invention

FIGS. 22A, 22B and 22C illustrate an additional alternative deviceconstructed in accordance with the principles of the present invention;

FIGS. 23A and 23B illustrate an alternative venturi device in whichsuction created by the venturi throat is used to draw air through aturbine to generate electrical energy;

FIGS. 24A and 24B are similar to the alternative device in FIGS. 23A and23B, but the suction force is used to draw water through the turbine;and

FIGS. 25A and 25B illustrate an alternative embodiment in which liftingmeans is incorporated into the buoy to modify the position of theventuri and or the generator.

DETAILED DESCRIPTION

This invention provides an improved design for wave energy devices ofthe types proposed by Bichard and Heck, as well as an improved designfor all other varieties of venturi-based wave energy devices. Inaddition, this invention provides a method for optimizing the design ofthe venturi component used in these types of devices. This optimizationis made with respect to the degree to which the design's resultingventuri effect will accelerate the water flowing through the submergedcomponent of the power-generation system, e.g. a turbine or suctiondevice.

The preferred embodiment of this invention utilizes a venturi tubeembedded within an outer cylindrical housing. The preferred embodimentof this invention rigidly connects the submerged venturi tube to thebuoy above through multiple struts arranged about the periphery of thetube and the buoy. The preferred embodiment of this inventionincorporates a venturi throat whose cross-sectional area is specificallydesigned to optimize the amount of power extracted from a portion ofocean perturbed by waves with specific patterns of height and period,and with respect to the selected venturi throat depth.

For a fuller understanding of the nature and objects of the invention,reference should be made to the following detailed description, taken inconnection with the accompanying drawings, in which:

FIG. 1 is an illustration of a wave-energy device proposed in the priorart, and comprises a turbine having a propeller 20 connected to a hub 22mounted on a shaft 24 suspended beneath a buoy 23 disposed on thesurface 28 of the ocean. This device seeks to exploit the diminution ofwave motion with depth. As the buoy rises and falls, the submergedturbine is moved up-and-down through the relatively still waters beneaththe waves, causing the turbine to rotate, and thus causing the shaft ofan attached generator to rotate, thus generating electrical power.

FIG. 2 shows a prior art device disclosed in U.S. Pat. No. 4,447,740. Inthis illustration, “D_(t)” denotes the diameter of the opening of thefrusto-conical lip that Heck specifies as an optional addition to eachend of the cylindrical shroud that surrounds the turbine. “D_(h)”denotes the diameter of the cylindrical shroud surrounding the turbine.“D_(h)” also denotes diameter of the turbine located within the shroud.

FIG. 3A shows one embodiment of the novel optimized, device of thepresent invention. This embodiment of the present invention is intendedto generally resemble the Heck device except with respect to theconstruction of the venturi. In this illustration, “D_(t)” denotes thediameter of the mouth of the venturi tube and is equal to the “D_(t)” ofFIG. 2. “D_(m)” denotes the diameter of the narrowest portion of theventuri tube, i.e. its “throat”. “D_(m)” also denotes the diameter ofthe turbine located therein.

FIGS. 3B and 3C are illustrations of another embodiment of the presentinvention, i.e. of a wave energy device utilizing a submerged venturidevice which is optimized for the purpose of extracting a maximal amountof power from the ocean.

Venturi device 30 including a housing 30 a and a venturi 31 disposedtherein is suspended by cables 25 beneath a flotation module 26. Theventuri device's distance beneath buoy 26 is held constant, and tensionis maintained in cables 25 due to the weight of device 30 and of anyoptional attached supplemental weight suspended beneath it by cables.The cables may be flexible or rigid.

The venturi device's efficiency is maximized by suspending it below, orat least as near as possible to, the wave base characteristic of thelongest wavelength of wave for which energy conversion is desired. Thispreferred depth would typically range from twenty (20) to one hundred(100) meters. FIGS. 3B and 3C are not drawn to scale.

As venturi device 30 rises, water flows through venturi 31 fromtop-to-bottom. As venturi 30 sinks, water flows through venturi 31 inthe opposite direction. As the water flows through the venturi 31 itsrate of axial flow (i.e. its speed) increases in proportion to thereduction in the cross-sectional area of the venturi. For example, asthe cross-sectional area of the venturi 31 is halved, the speed of thewater flow is doubled.

A type of turbine suitable for use within a venturi is the family ofturbines known as free flow or kinetic turbines. Simple propeller 21 isindicated in FIG. 3C for convenience.

As water is constrained to flow through venturi 31 the turbine bladesmust rotate. The blades are joined to a hub (not shown) and the hubrotates conjointly with the turbine central shaft 24 a. If the turbineblades are bi-directional, shaft 44 rotates in the same directionregardless of whether water is entering venturi 31 from the top orbottom. Only the angular speed of rotation varies as the tube moves upand down through the water—the angular direction of rotation does notvary.

As venturi device 30 rises and falls in the water beneath the surface,water enters the venturi 31 alternately from the top and bottom, andcompels propeller 21 to spin. Shaft 27 is connected by connector 42 a toflexible but non-stretchable cable 44, and the flexible cable isconnected by connector 42 b to central shaft 24 a of buoy 26 whichcentral shaft is connected to generator 46 or some other energyconversion device.

Accordingly, rotation of propeller 21 causes rotation of central shaft27, cable 44, buoy shaft 24 a and hence the generator 46.

In this manner, some of the energy of the deep-water waves which compelbuoy 26 and its attached venturi device 30 to rise and fall is convertedto mechanical energy. The potential energy of venturi device 30increases with its height. Some of the venturi tube's potential energythat remains after a wave has passed is converted into additionalmechanical energy as buoy 26 and its attached venturi 30 fall and againcause the rotation of propeller 21, central shaft 24, cable 44, buoyshaft 24 a and generator 46. All or most of the mechanical energycreated during the rising and falling of venturi device 30 is availablefor conversion into electrical energy.

FIGS. 4A and 4B are illustrations of the preferred embodiment of thisinvention. As is therein shown a venturi device 50 is disposed beneath aflotation member 52 by a plurality of rigid struts 54, 56, 58 and 60.The venturi device includes an upper section 62 and a lower section 64.The upper and lower sections define an entrance to a venturi tube 66which is embedded within the venturi device 50. The venturi tube 66 hasthe cross-sectional area thereof reduced toward the mid point betweenthe section 62 and 64 to define the throat 68 of the venturi tube 66.This construction is illustrated by the tapered wall 70 connecting thelower section 64 with the throat 68. Disposed at throat 68 of theventuri tube 60 is a means for generation of motion 72 such for exampleas a propeller or other similar device. The propeller 72 is connected bya rigid shaft 74 to an electrical generator 76. As the propeller movesresponsive to up and down movement of the flotation member 52, thepropeller rotates and through the connection 74 causes the generator 76to rotate thereby generating electrical energy.

FIG. 5 is an illustration of a turbine enclosed within a venturi device.The venturi device will accelerate the water flowing through the turbineby means of a venturi effect. FIG. 5 is an illustration of arepresentative venturi device (i.e. a venturi tube in this case) and ofone possible power-extraction system (i.e. a turbine in this case)useful in the extraction of power from a moving fluid (e.g. likeseawater). The venturi tube in this figure is not drawn to scale.

In this illustration, “Dm” denotes the diameter of the mouth of theventuri tube, while “Dt” denotes the diameter of the tube's throat. “Vm”denotes the speed of the water entering the tube (from below in thiscase) while “Vt” denotes the accelerated speed of the water flowingthrough the throat of the tube, and through the turbine located there.“Pt” denotes the power extracted by the turbine from the water flowingthrough the throat of the venturi tube.

FIG. 6 illustrates the effect of reducing the diameter of a venturidevice's throat, relative to the diameter of its mouth, on severalimportant aspects of its behavior. Reducing the relative throat diameter(or, equivalently, reducing the cross-sectional area of the venturithroat relative to the cross-sectional area of the venturi mouth)increases the degree to which the speed of the water is amplified (i.e.the line labeled “relative water speed”). Also, since the amount ofpower which can be extracted from flowing water is proportional to thecube of the water's speed, reducing the relative throat diameter of theventuri device, and thus increasing the speed of the water passingthrough it, results in a substantial increase in the amount of power(i.e. kinetic energy) which is available for extraction within thatwater.

FIG. 6 does not impose any upper limit on the speed to which the waterflowing through a venturi device can be accelerated. In truth, such anupper limit exists and is referred to as the “choke speed” of the water.The choke speed will vary primarily with the pressure of the waterentering the venturi device, and will therefore tend to increase as thedepth of the venturi device below the surface increases.

The data in FIG. 6, i.e. in the absence of a choke limit providing anupper bound on the degree to which the speed of the water can beaccelerated, would suggest that with an infinitely small venturi throat,one might be able to extract an almost infinite amount of energy.Clearly, that would be absurd. A consideration of the role of the chokespeed is vital in determining the optimal throat diameter in a practicalventuri device,

Another tradeoff to be considered in identifying an optimal venturithroat diameter is the fact that the amount of power that a turbine canextract from a flowing volume of water is proportional not only to thecube of the water's speed, but also to the cross-sectional area of theflowing water (for example, to the cross-sectional area of a turbinelocated in the throat of the venturi and used to extract the power).Thus, as the throat of a venturi grows smaller, the speed of the waterincreases (up to the choke speed), which increases the power availablefor extraction, but the cross-sectional area of the water flowing withthat increased speed decreases, which reduces the amount of power forextraction.

FIG. 7 is a graph illustrating the relationship between the depth of aventuri tube (i.e. the depth of a venturi tube's throat) and the venturitube's choke speed. A venturi's choke speed increases with increasingdepth due to a corresponding increase in water pressure.

The temperature of the seawater in which a venturi device will operatewill typically range from −2° C. to 30° C. Within this range oftemperatures the vapor pressure of water, and hence the choke speed of aventuri device, will vary only slightly. Therefore, the choke speed of aventuri device will only vary to a minor, if not negligible, extent withrespect to the temperature of the seawater entering a venturi device.Expected seawater temperature can be incorporated in to the optimizationprocess described in this invention if so desired by those skilled inthe art. However, for the sake of improved clarity, a seawatertemperature of 20° C. has been assumed in the disclosure of thisinvention.

FIG. 8 is a graph illustrating the maximum amount of available power(i.e. the line labeled “optimal available power”), which can be achievedthrough the selection of an optimal relative venturi throatcross-sectional area (relative to the cross-sectional area of theventuri mouth, and expressed in the graph as the diameter of anequivalent circular cross-sectional area), with respect to a range oflikely choke speeds. Choke speed (m/s) is on the abscissa, optimalrelative throat diameter on the left ordinate and optimal power inkilowatts per square meter (kW/m²) on the right ordinate. As the chokespeed increases, the optimal relative throat cross-sectional areadecreases, because the degree to which the water can be acceleratedincreases. The optimal amount of power available, in the water flowingthrough a venturi device, with a suitably optimized venturi throatincreases from 50 to 650 kW/m² (i.e. per m² of the cross-sectional areaof the venturi device's mouth) over the indicated range of choke speeds.The actual amount of power available can be determined by multiplyingthe amount of power available per square meter, as specified in thegraph, by the cross-sectional area of the mouth of a venturi device withthe specified relative throat diameter (or the equivalent relativethroat cross-sectional area).

As an example, let's consider the graph in FIG. 8. Let's assume that wewant to know the optimal amount of power available to a submergedventuri device, and the corresponding relative venturi throat diameterneeded to achieve that optimal level of available power, when ourventuri device will operate in waters characterized by a choke speed of30 m/s (i.e. at a depth of about 40 meters).

On the graph shown in FIG. 8, we find that the optimal available powercorresponding to a choke speed of 30 m/s is about 265 kW/m². We alsofind that this optimal amount of power is associated with a relativeventuri throat diameter of about 0.21.

If we want to calculate the actual throat diameter and available powerfor a specific venturi device, we need to scale each of the relativevalues specified in FIG. 8 by the appropriate attribute of the mouth ofthe actual venturi device. If we have a venturi device with a mouthpossessing a cross-sectional area of 3 m², then the corresponding amountof available power when such a device operates in waters with a chokespeed of 30 m/s is:3 m²*265 kW/m²=795 kWThe equivalent diameter (i.e. “Dm”) of a venturi mouth with across-sectional area of 3 m² is:(ΠDm ²)/4=3 m², so Dm=1.95 meterTherefore, remembering that the optimal relative throat diameter is0.21, we may calculate the corresponding diameter of the throat of ouractual venturi device (“Dt”):Dt=0.21*1.95 m=0.41 meterThe corresponding optimal cross-sectional area (i.e. “At”) of theventuri throat for our sample venturi device is:At=Π(0.41 m)²/4=0.13 m

FIG. 9 is a graph illustrating the optimal amount of available power,which can be achieved through the selection of an optimal relativeventuri throat diameter (or a corresponding optimal venturi throatcross-sectional area), with respect to a range of likely wave heights.Wave height is shown on the abscissa, optimal relative throat diameteron the left ordinate and optimal power on the right ordinate. As thewave height increases, the optimal relative throat diameter (withrespect to the diameter of the mouth in an equivalent venturi tube)increases. The optimal amount of power available per square meter of thecross-sectional area of the venturi mouth, in the water flowing throughthe throat of an optimized venturi device, increases from 0 (in theabsence of waves) to 700 kW/m² (with respect to waves with a height of15 meters). A more likely range of wave heights would be 3 to 6 meters,with respect to which the corresponding optimal amounts of availablepower would be 138 to 277 kW/m².

FIG. 10 is a graph illustrating the optimal amount of available power,which can be achieved through the selection of an optimal ratio of thecross-sectional areas of venturi throats to mouths, with respect to arange of likely wave periods. Wave period is shown on the abscissa,optimal relative throat diameter on the left ordinate, and optimal poweron the right ordinate. As the wave period decreases (and the energy ofthe waves therefore increases), the optimal relative throat diameter(with respect to the mouth diameter in an equivalent venturi tube)increases. The power available in the water flowing through the throatof an optimized venturi device increases from 100 to 1470 kW/m² as thewave period decreases from 15 seconds down to 1 second. A more likelyrange of wave periods would be 11 to 7 seconds, and the correspondingoptimal amounts of available power would be 134 to 210 kW/m².

FIG. 11 is a graph illustrating the relationship of the power available(i.e. the line labeled “relative available power”) within a venturidevice with respect to a range of possible relative venturi throatdiameters (i.e. ranging from 1.0, i.e. a throat diameter equal to thediameter of the venturi mouth, down to 0, the absence of any throat atall). This graph illustrates the basic mechanism for selecting anoptimal venturi throat diameter with respect to a specific set of waveconditions.

The relationships expressed in this graph apply not only to venturitubes, but also to any venturi device. The square of the indicated“Relative Throat Diameter” provides the relative cross-sectional area ofthe throat of any venturi device relative to the cross-sectional area ofthe device's mouth. The graph's use of a “Relative Throat Diameter” isbased on the assumption of a radially symmetrical venturi tube, but thedata in the graph applies with equal force to venturi device of any formor design.

Note that FIG. 11 reveals an optimal relative diameter for the throat ofthe venturi device (and a corresponding optimal relative cross-sectionalarea) when driven by waves of the specified kind, in water characterizedby the specified choke speed. This optimal throat diameter, and/orcross-sectional area, is a unique value with respect to the followingcombination of wave height, wave period and choke speed.

The graph in FIG. 11 is based on the following assumptions:

-   -   a choke speed of 25 m/s,    -   a wave height of 4 meters, and    -   a wave period of 8 seconds.

With respect to these assumptions, the maximum available power occurswhen the relative throat diameter is 0.23, which is equivalent to arelative throat area of 0.053. With respect to this optimal venturidevice configuration, and with respect to the specified wave height,wave period, and choke speed, the available power in the water flowingthrough the throat of the venturi tube would be increased by a factor of280× with respect to the amount of power available in the unacceleratedwater outside the venturi device. With respect to the wave conditionsspecified above, the amount of power available in the unacceleratedwater flowing in to the venturi device's mouth is 0.661 kW/m².Therefore, the actual amount of power available with respect to theoptimal relative venturi throat diameter of 0.23 is:0.661 kW/m²*280=183 kW/m²183 kW/m² is the optimal, or maximal, amount of power which can be madeavailable by a venturi device submerged in water characterized by thespecified choke speed when the device is driven by waves with thespecified height and period.

FIG. 12 is a graph like the one in FIG. 11. However, this graph of therelationship of the power available with respect to the relative venturithroat diameter is with respect to a different set of wave conditionsand choke speed.

Note that FIG. 12 reveals an optimal relative diameter for the throat ofthe venturi device (and a corresponding optimal relative cross-sectionalarea) when driven by waves of the specified kind, in water characterizedby the specified choke speed. This optimal throat diameter, and/orcross-sectional area, is a unique value with respect to the followingcombination of wave height, wave period and choke speed.

The graph in FIG. 12 is based on the following assumptions:

-   -   a choke speed of 30 m/s,    -   a wave height of 6 meters, and    -   a wave period of 7 seconds.

With respect to these assumptions, the maximum available power occurswhen the relative throat diameter is 0.275, which is equivalent to arelative throat area of 0.076. With respect to this optimal venturidevice configuration, and with respect to the specified wave height,wave period, and choke speed, the available power in the water flowingthrough the throat of the venturi tube would be increased by a factor of136× with respect to the amount of power available in the unacceleratedwater outside the venturi device. With respect to the wave conditionsspecified above, the amount of power available in the unacceleratedwater flowing in to the venturi device's mouth is 3.33 kW/m². Therefore,the actual amount of power available with respect to the optimalrelative venturi throat diameter of 0.275 is:3.33 kW/m²*136=455 kW/m²455 kW/m² is the optimal, or maximal, amount of power which can be madeavailable by a venturi device submerged in water characterized by thespecified choke speed when the device is driven by waves with thespecified height and period.

FIG. 13A displays a cross-sectional profile of a typical deep-waterwave, as it might appear if it were sliced along a plane parallel to itsdirection of propagation and normal to the surface of the ocean. Thewave illustrated in this figure has a height of 4 meters and a period of8 seconds. Note that the wave begins and ends at points described as“troughs” where the water is at its lowest level during the wave cycle.Also, note that the wave reaches a “peak” mid-way through its period.The vertical distance between the troughs and the peak is the measure ofthe height of a wave.

FIG. 13B displays the relationship of the vertical speed of the water atthe surface of a wave to the height of that water along the wave'sprofile. The same wave height displayed in FIG. 13A is also shown thisfigure. However, FIG. 13B includes a line denoting the vertical speed ofeach point along the surface of the corresponding portion of the wave'sprofile. Note that the speed reaches it maximum at the points on thewave's surface that represent the vertical midpoints of the wave'sprofile. In the sample shown, the maximum speed of 1.57 meters persecond occurs at 2 and 6 seconds after the wave's trough. Theserepresent one- and three-quarters of the wave's progress towards itsnext trough.

FIG. 13C displays, for reference, the same wave profile shown in FIGS.13A and 13B. FIG. 13 C also includes the same vertical speed profile forthe reference wave, which ranges from 0 to 1.57 m/s. FIG. 13C includes aline, i.e. labeled “amplified speed”, which represents the speed whichwould characterize the water traveling through the throat of a venturidevice which possessed a ratio of mouth-to-throat cross-sectional areas,i.e. a “venturi factor”, of 18.9. This amplified speed profile rangesfrom 0 to 30 m/s. In other words:[input speed 0 to 1.57 m/s]*[venturi factor of 18.9]=[throat speed 0 to29.7 m/s]

FIG. 13C also displays what the actual water-speed profile, of the waterflowing through the throat of a venturi device with a venturi factor of18.9, would be if the water entering the venturi device mouth wascharacterized by a choke speed of 25 m/s. This is the choke speed onemight expect to encounter with a venturi device operating at a depth ofabout 22 meters.

FIG. 13D displays the amount of power that would be available in thethroat of a venturi device with a venturi factor of 18.9, when it isdriven by waves with a height of 4 meters and a period of 8 seconds,when the water flowing through the venturi device has a choke speed of25 m/s. Note that the amount of available power is truncated at a levelof 424 kW/m². This truncation, or upper-limit, of the level of availablepower is a direct consequence of the truncation, or upper-limit, of theamplified speed of the water flowing through the throat of the venturidevice.

Note that the power levels displayed in this graph are specified interms of power per square meter (i.e. kW/m²). This is because thesepower levels are relative to the total size of the venturi device. Inparticular, these power levels are relative to the amount of water thatwill enter a particular venturi device. For example, a venturi devicethrough which flows twice the volume of water as that which flowsthrough another venturi device will likewise have twice as much poweravailable for extraction. The power levels specified in this graph, andin many of the other graphs referred to in this patent, will beexpressed in terms of kW/m², where the area is in relation to thecross-sectional area of the venturi mouth of any particular venturidevice. The actual power level associated with any particular devicewill be determined by multiplying the cross-sectional area of theventuri device's mouth by the relative amount of power specified.

FIG. 14 shows the relationship between the actual speeds and powerlevels (still relative to the cross-sectional area of the venturidevice's mouth) and the relative throat diameters with respect to aventuri device operating in waves with a height of 4 meters, a period of8 seconds, and a choke speed of 25 m/s. Note the power level associatedwith the ambient water entering the mouth of the venturi device (i.e.before any amplification of its speed has occurred) is 0.661 kW/m². Alsonote that the power level that would characterize a Heck wave energydevice, which possesses a relative venturi throat diameter of 0.862,would be 1.2 kW/m², an 80% improvement. Finally note that the maximumpossible power level associated with a venturi device optimizedaccording to the principles of this invention would be 184 kW/m², animprovement of 28,000%. An optimized venturi device can make available15,000% more power than an equivalent Heck device.

Also note in FIG. 14 that the optimal relative throat diameter (i.e.0.23) is slightly less than the diameter at which the speed of the waterpassing through the throat of the venturi device first begins to reachand/or exceed the choke speed (i.e. at 0.25).

FIG. 15 shows four power optimization curves, similar to the curveillustrated for 4-meter waves in FIG. 14. These four curves of availablepower correspond, respectively, to waves with heights and periods of:

-   -   2 meters and 7 seconds,    -   4 meters and 8 seconds,    -   6 meters and 9 seconds,    -   8 meters and 10 seconds

Note that, with respect to each unique wave type, there is acorresponding unique relative venturi throat diameter that would resultin an optimal amount of power being made available for extraction.Obviously, an actual wave energy device deployed in a real environmentwill be subjected to a variety of wave types. Therefore, the selectionof the one relative venturi throat diameter for a particular wave energydevice must balance the effects of that particular diameter on theoverall power of the device.

FIG. 16 shows the results of optimizing the relative venturi throatdiameter with respect to two different sets of expected wave conditions.(Note the assortment of wave types contributing to each wave conditionis admittedly rudimentary. However, we are keeping this simple for thepurpose of facilitating understanding in the optimization principlesinvolved.)

The set of wave types labeled as “calm oceans” includes:

-   -   60% of waves with a height of 2 meters and a period of 7        seconds,    -   30% of waves with a height of 4 meters and a period of 8        seconds,    -   8% of waves with a height of 6 meters and a period of 9 seconds,    -   2% of waves with a height of 8 meters and a period of 10        seconds.

The set of wave types labeled as “active oceans” includes:

-   -   10% of waves with a height of 2 meters and a period of 7        seconds,    -   20% of waves with a height of 4 meters and a period of 8        seconds,    -   60% of waves with a height of 6 meters and a period of 9        seconds,    -   10% of waves with a height of 8 meters and a period of 10        seconds

FIG. 17 shows the results of optimizing the relative venturi throatdiameter with respect to a combination of individual “ocean conditions”which might characterize a deployment site over the course of a year.This optimization is with respect to the following balance:

-   -   60% (or about 7 months) of calm oceans, and    -   40% (or about 5 months) of active oceans.

An actual deployment site might include complicated wave conditions overthe course of a year. Conditions might even vary from year to year. Inan actual optimization, one would likely catalogue the frequency withwhich each distinct wave type is observed at a particular deploymentsite (with whatever resolution in terms of height and period is desired)over the course of a suitable period of time, e.g. over the course of ayear. The amount of power derived from each wave type could then beweighted by the frequency with which it was observed, or with which itis expected to be observed in the future, and the sum of the weightedpower contributions associated with each wave type can then be used tocompute the overall power level which would be expected with respect toeach possible relative venturi throat diameter.

FIG. 18 is a table comparing a Heck venturi device with an equivalentdevice optimized according to the principles of this invention. Thecomparison is made on the basis of devices with a 7-meter diameterventuri device mouth, whose vertical oscillations are being driven bywaves with heights of 4 meters, and periods of 8 seconds, in waters witha choke speed of 25 m/s.

FIG. 19 shows a comparison between the amount of power that would bemade available) for extraction by a Heck wave energy device and by anequivalent device optimized according to the object of this invention.The power levels displayed in this figure are displayed relative towaves with heights ranging from 0 to 10 meters (and periods of 8seconds, and choke speeds of 25 m/s). Note that the relative venturithroat diameter of the Heck device remains constant at 0.862, while theoptimal diameter varies continuously from 0.01 (with respect to verysmall waves) to 0.36 (with respect to the most energetic waves). Thepower made available within a Heck wave energy device is uniformly, andsubstantially, less than that made available by an equivalent optimizeddevice.

FIG. 20 is an alternate type of venturi device to which this inventionwould apply with equal force. It utilizes a venturi tube in which eachcross-sectional area normal to the axis of the venturi tube isrectangular instead of circular. It also uses, as its power extractionmechanism, a turbine utilizing an axis of rotation normal to the axis ofthe venturi tube. This type of turbine extracts energy from the waterflowing through throat 131 of venturi tube 130 regardless of thevertical direction of the water's travel. Water entering either mouth ofventuri tube 130 induces the same rotational motion inperpendicular-axis turbine 120 a. Such a turbine can be attacheddirectly to an alternator or generator 146 by a shaft 124 a or theturbine's rotational energy can be transmitted by any combination ofsolid (rigid) or flexible shafts to buoy 26.

If an alternator or generator 146 is located within the sidewalls ofventuri tube 130 as depicted in FIG. 20, the electrical energy generatedin response to the rotation of the perpendicular-axis turbine 120 a istransmitted to the surface via one or more electrical conductors. Suchconductors extend along one or more of the cables or struts 54-60supporting venturi tube 130 beneath buoy 26. The optimization of thistype of venturi device would also fall within the scope of this patent,as would the optimization of any other type of submerged venturi device.

FIG. 21 is another alternate type of venturi device to which thisinvention would apply with equal force. It utilizes a pair ofwedge-shaped venturi devices that act in concert to spin an embeddedturbine. The optimization of this type of venturi device would also fallwithin the scope of this patent, as would the optimization of any othertype of submerged venturi device.

FIGS. 21A and 21B depict one of many possible embodiments of the novelventuri wave-energy device that are within the scope of this invention.FIG. 21B is a cross-sections view of housing 168 taken along line21B-21B in FIG. 21A.

Water wheel 164 is mounted for rotation about axle 165 in housing 168that includes two substantially parallel vertical walls 166A and 166B.Housing 168 has two compartments that are in fluid communication withone another. The first compartment is defined by sidewall 166A, frontwall 168A, and back wall 168B. Front and back walls 168A, 168B convergetoward one another from top to bottom, creating a venturi effect at thebottom of said first compartment. The second compartment is defined byside wall 166B, front wall 170A and back wall 170B. Front and back walls170A, 170B diverge from one another from top to bottom, creating aventuri effect at the top of said compartment.

Axle 165 of water wheel 164 is positioned in the center of housing 168so that half of said water wheel is in the first compartment and half isin the second compartment.

The left compartment as viewed in FIG. 21A receives water entering fromthe top and accelerates it as it moves toward the bottom, due to thedecreasing cross-sectional area of the left compartment. Also any waterentering the right compartment from the bottom accelerates as it flowsthrough the right compartment's decreasing bottom to top cross-sectionalarea.

FIG. 22A is yet another alternate type of venturi device to which thisinvention would apply with equal force. It utilizes a semi-rigid venturishroud 133 having ribs 156 and fabric 158, which could, in someembodiments be collapsible. This type of venturi device, unlike thetypes discussed earlier, would only generate significant amounts ofpower when pulled up by its associated flotation device. A turbine 120Bis disposed in the throat 160 of the venturi and is connected by a shaft124B to a generator 146B. The venturi shroud might fully or partiallycollapse as the venturi device descends on the falling side of a passingwave. The optimization of this type of venturi device would also fallwithin the scope of this invention, as would the optimization of anyother type of submerged venturi device.

FIG. 22B illustrates how such an alternative embodiment of a venturidevice as shown in FIG. 22A, i.e. one employing a collapsible venturishroud, might fit inside a canister 155 for storage, and perhaps as anaid to deployment. Such a portable optimized venturi device might beuseful as a power supply for buoys or life rafts.

FIG. 22C illustrates how such an alternate embodiment of a venturidevice might operate in conjunction with a buoy.

A further discussion of FIGS. 22A-C follows. A preferred embodiment ofthe full-sized venturi-pinwheel wave-energy device transmits its rotaryenergy to the surface through mechanical shaft or cable (44 in FIG. 3C)that is attached to the central shaft (27 of FIG. 3B) of the turbine (21of FIG. 3C). The mechanical rotational energy is converted intoelectrical energy with a generator mounted above the water line. Toadapt this technology to small, portable devices, a small water-proofgenerator 146 b is located near the turbine 120 b and shares a commonaxle 124 b with it.

The resulting power is transmitted to buoy 26 a through primaryelectrical cable 144 which may also support the venturi shroud assemblyas it hangs beneath buoy 26 a. The preferred embodiment of a portableversion of the venturi-pinwheel device includes central rigid support157 securing cable assembly 144 to the turbine assembly. Central rigidsupport 157 maintains the vertical alignment of venturi shroud 133 andturbine 120 b as the venturi shroud is pulled toward the surface by buoy26 a. The upward force provided by the buoy acts on the upper end ofrigid support 157, and the drag induced by the unfurled venturi shroud133 acts on the lower end of support 157. For the same reason that awind vane orients itself to point into the wind, the central rigidsupport, and its attached venturi shroud, are compelled to point towardthe buoy. Without this central rigid support, the orientation of theventuri shroud could be unstable, i.e., under the influence of watermoving past it as it rises, the shroud would tend to turn sideways and acollapsible shroud would tend to partially collapse.

Because of its small size, solid turbine blade 120 b (FIGS. 22A and 22B)is advantageous, instead of an articulating bi-directional turbine.Venturi shroud 133 funnels water into the turbine, increasing thewater's speed, while the buoy and turbine are rising. A preferredembodiment of the full-sized venturi-pinwheel wave-energy device has abi-directional venturi shroud allowing it to generate power when fallingas well as rising. These adaptations allow the portable embodiment ofthe turbine to extract a significant amount of power from the seawateronly while the buoy and turbine are rising.

It is also possible to construct a “miniaturized” version of thepreferred embodiment of this device, i.e., a bi-directional venturi tubeincorporating a bi-directional turbine. Such a device can utilize alocal water-proof generator or a shaft transmitting rotational energy toa buoy at the surface of the water. For some applications thisintermediate design may be advantageous. The scope of this disclosureincludes all variations in the sizes of the devices disclosed.

A preferred embodiment of a portable version of the venturi-pinwheeldevice, which incorporates a collapsible venturi shroud, also containsrigid collar 160 serving as the base for the collapsible venturi shroud133 to constrain its alignment. Propeller/turbine 120 b is positionedconcentrically with rigid collar 160 because the lumen of rigid collar160 is the narrowest part of the lumen created by shroud 133. Rigidframe members 156 have a first end pivotally secured to rigid collar 160in circumferentially spaced relation to one another.

FIG. 22B illustrates the configuration of the portable embodimentdepicted in FIG. 22A when it is incorporates a collapsible venturishroud and is stored within a canister 155. Rigid frame members 156 ofventuri shroud 133 pivot toward rigid central support 157 of the device,and venturi shroud fabric 158 collapses like a retracted umbrella. Sucha stored device may be slid out of storage canister 155 following theremoval of optional canister lid 62.

FIG. 22C depicts the portable embodiment of FIGS. 22A and 22B with smallbuoy 26 a. This embodiment has utility in connection with a life raft.When the assembly of FIGS. 22A and 22B is connected to buoy 26 a bycable 144, the rising and falling of the portable venturi shroudgenerates electrical power. A life raft itself can serve as the buoy.This portable embodiment has utility in providing electrical power todistress beacons, locator devices, water distillation equipment, and thelike.

FIG. 23A and FIG. 23B illustrate an alternate type of wave energydevice, and inclusive venturi device, to which this invention wouldapply with equal force. This wave energy device is similar to thatillustrated in FIGS. 3B and 3C but uses the reduced and/or eliminatedlateral pressure in the water flowing through the throat of an optimizedventuri device to create a sucking force. In this type of wave energydevice embodiment the suction created at 233 by the venturi throat isused to draw air through a turbine 229 located in the buoy 26 at thesurface. Such a device would likely incorporate one-way valves 234 toprevent water from rushing in to the pipes used to communicate thepartial or full vacuum to the turbine at the surface when the suction inthe venturi throat diminishes at or near the peaks and troughs of thewaves driving the device's motion.

FIG. 24A and FIG. 24B illustrate another alternate type of wave energydevice similar to that illustrated in FIGS. 23A and 23B, and inclusiveventuri device, to which this invention would apply with equal force.Like the device illustrated in FIG. 23, this device would exploit thesuction created in the throat of an optimized venturi device to extractpower from the ocean. This wave energy device however would use thesucking force to draw water through the turbine. Water would be able toenter the turbine through an inlet 224C, and a full or partial vacuumcreated by the suction in the venturi throat would be used to draw waterout of the turbine, thus causing it to spin. The advantage of thisdevice, over the one illustrated in FIG. 23, is that the pipe(s)connecting the venturi throat to the turbine would contain water insteadof air. Thus, when the suction diminished near the peaks and troughs ofthe waves driving the vertical motion of the device, there would little,if any, tendency on the part of the water in the venturi throat to rushin to the pipe(s). Thus, it might not be necessary to utilize one-wayvalves in this type of device.

5. Detailed Description of the Preferred Embodiment

5a. Basic Design

The preferred embodiment of this invention (see FIG. 4) incorporates abuoy 52 rigidly attached to a submerged, radially symmetrical venturitube, with a bi-directional turbine located in the throat of the venturitube. In the preferred embodiment, the venturi tube is attached to thebuoy by means of struts 54-60 located about the periphery of the tubeand buoy. In the preferred embodiment, the rotation of the submergedturbine causes the attached turbine shaft to rotate, which, in turn,causes the shaft of an attached alternator to rotate. In the preferredembodiment, the rotations of the alternator's shaft result in thegeneration of electrical power.

However, many alternate embodiments are possible for a wave energydevice that facilitates, and optimizes, its power extraction by means ofan optimized venturi effect. All such alternate embodiments are withinthe scope of this invention.

5b. Optimization of Venturi Effect for Waves of Constant Height

5b1. Assumptions

For the sake of illustration, we will discuss the optimization of theventuri effect created within a wave energy device of the typeillustrated in FIG. 4. The following discussions regarding theoptimization of the venturi effect would apply equally well, with onlyslight, if any, modification, to other embodiments of venturi-based waveenergy devices.

We will discuss the optimization of a venturi device from theperspective of a limiting, or maximum, overall device size. The types ofventuri-based wave energy devices being discussed here have maximumpractical sizes. However, the scope of this patent is not limited to thesize of the energy device and applies with equal force to devices of allsizes.

The diameter of a buoy employed in this type of device (or the maximumwidth of the ocean surface area displaced by such a floating component)should not exceed more than a small fraction of the wavelength of thewaves from which power is to be extracted if it is to remain optimal.Otherwise, the buoy will begin to “integrate” the wave's motion. Thatis, the amplitude of the buoy's vertical oscillations will begin todecrease with respect to the amplitude of the vertical oscillations ofthe waves passing beneath it. You can imagine that if a buoy's diameterwere twice as great as the wavelength of the waves passing under it,then it would be difficult for the buoy to move up-and-down at all. Thebuoy would overlay as many wave crests as wave troughs and the netresult would be little, if any, vertical movement.

However, it is much more likely that the diameter of a venturi-type waveenergy device will be limited by practical considerations related toconstruction, deployment and maintenance, rather than being limited byits tendency to integrate waves. For instance, there might be practicalconsiderations that dictate that the maximum diameter of a practicalwave energy device might be 7 meters.

Therefore, when we discuss varying the diameter of the throat of aventuri tube in order to optimize the venturi effect, and the resultingextraction of power, we will discuss that throat diameter relative to afixed (though arbitrary) diameter of the corresponding mouth of theventuri tube.

Furthermore, even though we will discuss the optimization of thediameter of the throat of a venturi device, relative to the diameter ofits mouth, the same discussion and optimization procedure could applywith equal validity to the cross-sectional area of the throat of aventuri device, relative to the cross-sectional area of its mouth. Wediscuss the optimization process relative to the diameters of apresumably radially symmetrical venturi tube. However, the same process,discussed in terms of the respective cross-sectional areas, would applyto the optimization of venturi devices which were not radiallysymmetrical, and for which a reference to a diameter would beinappropriate.

We will also frequently discuss the optimization process, and thevarious quantities related to that process, in terms made relative tothe cross-sectional area of the mouth of a venturi device. For instance,we will often express a power level as some amount of kilowatts persquare meter. Obviously, power levels are not usually expressed relativeto an area. We express such power levels as a level of powerproportional to the cross-sectional area of the mouth of the venturidevice under discussion. The actual power level can be obtained bymultiplying the relative level specified by the cross-sectional area ofthe mouth of the venturi device under discussion.

FIG. 5 illustrates a sample venturi device with a mouth of diameter “Dm”which we will assume to be fixed at some arbitrary value, and a throatof diameter “Dt” which we will vary in our effort to optimize theventuri effect influencing the power available for extraction from theturbine.

5b2. Competing factors

The optimization of a venturi device, with respect to the degree towhich it amplifies the speed of the water entering the venturi's mouth,involves two competing factors.

As the cross-sectional area of a venturi tube is reduced, the speed ofthe water that flows through that tube is increased. If you will examineFIG. 6 you will see a line (i.e. “relative throat area”) that specifiesthe relationship between the relative cross-sectional area of a venturitube's throat, and the corresponding relative throat diameter—bothquantities being “relative” to the corresponding attributes of theventuri tube's mouth. This also specifies the area which will be sweptby the blades, of any turbine operating therein. This area isproportional to the square of the throat's diameter. Furthermore, sincethe power generated by a turbine enclosed in the venturi tube's throatis proportional to the area swept by its blades, this same linespecifies how the amount of power that a turbine could extract fromwater will change as a consequence of changes to its diameter.

In FIG. 6 you will see a line (i.e. “relative water speed”) thatspecifies the relationship between the mouth-relative diameter of aventuri tube's throat and the relative speed of the water that will movethrough it (i.e. relative to the speed of the water that enters theventuri device). The water's speed is inversely proportional to thesquare of the diameter. (Actually, the degree to which the speed of thewater is amplified is equal to the area of the mouth divided by the areaof the throat. If you halve the area of the throat, relative to the areaof the mouth, then you double the speed of the water that will flowthrough it, relative to the speed of the water which enters the mouth.)

In FIG. 6 you will see a line (i.e. “relative available power”) thatspecifies the relationship between mouth-relative diameter of a venturitube's throat and the amount of power available in water moving throughthat throat at the corresponding speed. This is the power that will beavailable in the water flowing through the venturi tube's throatrelative to the power available in the water entering the venturi tube'smouth.

Finally, in FIG. 6 you will see a line (i.e. “relative device power”)that specifies the relationship between the mouth-relative diameter of aventuri tube's throat and the amount of power available per square meterof the cross-sectional area of a stream of water moving at a particularspeed. The “relative device power” is that “relative available power”(i.e. power per unit cross-sectional area) multiplied by thecross-sectional area of the venturi tube's throat. When thecross-sectional area of a venturi device's throat narrows, the waterspeeds up, which increases the amount of power available per unit ofcross-sectional area, but the total cross-sectional area availabledecreases, so a tradeoff exists. This tradeoff is what this inventionseeks to optimize.

The “relative device power” illustrated in FIG. 6 specifies how muchpower would be available for extraction by a turbine located in thethroat of a venturi tube relative to the amount of power that would beavailable by a turbine located in the mouth of the venturi tube. Theinteresting observation to note here is that even though a turbine in aventuri tube's throat would presumably be smaller than a turbine whichcould be located in a venturi tube's mouth (or simply located in thewater without benefit of a venturi tube as in Bichard), nevertheless,the amount of power which would be available for extraction by a turbinein the tube's throat would be much greater than the amount of powerwhich would be available for extraction by a turbine in the tube'smouth, or a turbine outside the tube all together. This increase in theoverall amount of power available for extraction is a consequence of thecorrelation between the amount of power available and the cube of thewater's speed.

The lines shown in FIG. 6 would suggest that a venturi tube throat witha microscopically small diameter would be capable of producing an almostinfinite amount of power. The reason why the graph in FIG. 6 suggeststhis nonsensical possibility is because this graph fails to account forthe “choke speed” of the water that is moving through a venturi tube(explained below).

The choke speed of the water results in an optimal relative venturithroat diameter that is significantly greater than zero.

The optimal diameter of a venturi tube throat in a venturi-based waveenergy device is influenced by the choke speed (i.e. the depth) of thewater in which the venturi tube will operate, the height of the waveswhich will power the vertical oscillations of the venturi tube, and theperiod of those waves. This invention provides a method of optimizingthe performance of a venturi-based wave energy device with respect tothese factors.

5b3. Venturi Choke Speed

With respect to any given water pressure (i.e. water depth) there is amaximum speed to which the water can be accelerated by a venturi tube,or venturi effect. This maximum water speed is called the “choke speed”of the venturi tube, and the magnitude of the choke speed dependsheavily upon the water's pressure (or depth). When the speed of waterflowing through a venturi tube would, but fails, to exceed the tube'schoke speed, that condition is called “choked flow”.

FIG. 7 provides a graph illustrating the relationship of a venturitube's choke speed to the depth of the venturi tube's throat. Thealgorithm used to calculate the choke speed of a venturi tube as afunction of depth is not explained in this patent, but it will befamiliar to anyone skilled in the art.

A venturi tube accelerates the speed of the water moving through it byconverting some of the omni-directional kinetic energy (i.e. “pressure”)of the water entering the tube into additional speed of the overallwater flow. However, when this speeding of water flowing through aventuri tube occurs, the lateral pressure of the water, i.e. thepressure of the water normal to the axis of flow, decreases by a similaramount. In this way, energy is, as it must be, conserved. Thus, aventuri tube aligns the random motions of the water molecules enteringthe tube so that more and more of those water molecules move indirections parallel to the axis of the tube. So, even though the motionsof individual water molecules are no more energetic when travelingthrough a venturi tube, the macroscopic flow of the water travelingparallel to the axis of the venturi tube, i.e. the kinetic energy of themacroscopic flow, increases greatly.

This decrease in the lateral pressure of fluids moving through a venturitube is why these tubes are useful in creating a homogeneous dispersionof materials within a fluid. For instance, the carburetor in anautomobile uses a venturi tube to facilitate the injection of fuel intoan accelerated stream of air, thus creating a homogeneous mixture of airand fuel that is suitable for combustion. It is the reduced lateralpressure created in the flow of air passing through the venturi tube ofa carburetor that allows the fuel to disperse so evenly.

Or, in other words, the fuel disperses so evenly in the air, as the airpasses through a venturi tube, because the fuel doesn't encounter anyresistance to its motion as it enters the stream of air from a directionnormal to the axis of the venturi tube.

For a wave energy device, like the one comprising the preferredembodiment of this invention, and illustrated in FIG. 4, the maximumspeed to which the venturi tube will be able to accelerate the waterwill depend largely on the depth of the venturi tube's throat.

The speed of the water flowing through the throat of a venturi tube is amultiple of the original speed of the water entering the tube. Themagnitude of this multiplying factor (i.e. this “venturi factor”) isinvariant with respect to any particular venturi tube design, and equalsthe ratio of the cross-sectional areas of the mouth and the throat. Forexample, if the cross-sectional area of the throat is one-tenth thecross-sectional area of the mouth, then the venturi factor, by which thespeed of the water entering the tube is multiplied, is equal to 10×(i.e. 1/0.1=10).

However, the speed of the water entering the mouth of the venturi tube,when multiplied by the venturi factor, cannot exceed the choke speed ofthe water.

At a certain point, as the speed of the water closely approaches thechoke speed of the venturi tube, the pressure of the water will fallbelow the water's vapor pressure. At that point “cavitation” will occur.This means that the water will flash boil and create bubbles of gaseouswater vapor. Care must be taken that cavitation not be allowed to causepitting and wear on the turbine and on the walls of the venturi throat.

5b4. Optimum Determined with Respect to Choke Speed

FIG. 8 shows the relationship between the maximum amounts of power thatcan be made available through the application of this invention (i.e.the line labeled “optimal available power), relative to the choke speedof the water in which the venturi device will operate. The data in FIG.8 are based on a wave height of 4 meters and a wave period of 8 secondsand the determination of an optimal relative venturi throat diameterwith respect to each choke speed (i.e. the line labeled “optimalrelative throat diameter”).

The maximum amount of power that can be made available for extractionwithin the throat of a venturi device increases from a low of 50 kW/m²when the choke speed is about 13 m/s (the choke speed characteristic ofthe water at the surface of the ocean), to a high of 650 kW/m² when thechoke speed is about 47 m/s (the choke speed characteristic of water ata depth of about 100 meters). Further increases in the maximum amount ofpower available for extraction in a venturi device can be achievedthrough further increases in the depth, and corresponding choke speed,of the water in which the venturi device operates. The maximum depthspecified in FIG. 8 is an arbitrary value and does not represent anupper limit.

It is more likely that the submerged venturi devices will operate inwaters characterized by choke speeds ranging from 20 to 30 m/s. Withrespect to this range of choke speeds, the maximum amount of power thatcan be made available for extraction within the throat of a venturidevice will range from 120 to 265 kW/m², respectively.

A wave energy device with the same overall size, and differing only inthe cross-sectional area of its throat and embedded turbine (if any),can generate substantially more power with every increase in the depthof its attached venturi device. Of course, there are practicalconsiderations, such as weight, stress, environmental concerns, etc.,that may make a relatively modest depth more desirable. Also, if a waveenergy device is deployed over a continental shelf then the restricteddepth of the water will limit the depth at which the venturi device canoperate.

Note: The power levels discussed above, and below, when expressed interms of kW/m² are referring to the amount of power available forextraction from each square meter of the cross-sectional area of themouth of a venturi device. If a venturi device's mouth is larger, thenproportionately more power can be extracted from a similarly designedventuri device.

5b5. Optimum Determined with Respect to Wave Height

FIG. 9 shows the relationship between the maximum amounts of power thatcan be made available through the application of this invention,relative to the height of the waves driving the vertical oscillations ofa venturi device. The data in FIG. 9 are based on a choke speed of 25m/s and a wave period of 8 seconds.

The maximum amount of power that can be made available for extractionwithin the throat of a venturi device, optimized according to the objectof this invention, increases from zero, when there are no waves presentto drive the submerged venturi device, to a high of almost 700 kW/m²when the venturi device is driven by waves with a height of 15 meters.Of course, waves with heights exceeding 15 meters would offer theopportunity make even higher amounts of power available for extraction.The maximum wave height specified in FIG. 9 is an arbitrary value anddoes not represent an upper limit.

It is more likely that waves with heights ranging from 3 to 7 meterswould drive the vertical oscillations of a submerged venturi device.With respect to this range of wave heights, the maximum amount of powerthat can be made available for extraction within the throat of a venturidevice will range from 140 to 320 kW/m², respectively.

A wave energy device with the same overall size, and differing only inthe cross-sectional area of its throat and embedded turbine (if any),can generate substantially more power when driven by waves of greaterheight.

5b6. Optimum Determined with Respect to Wave Period

FIG. 10 shows the relationship between the maximum amounts of power thatcan be made available through the application of this invention,relative to the period of the waves driving the vertical oscillations ofa venturi device. The data in FIG. 10 are based on a wave height of 4meters and a choke speed of 25 m/s.

The maximum amount of power that can be made available for extractionwithin the throat of a venturi device, optimized according to the objectof this invention, increases very rapidly when the wave period becomesless than 4 seconds—a very unlikely prospect for waves with a height of4 meters. The maximum amount of power available for extraction when theventuri device is driven by 4 meter waves with a period of 15 seconds isabout 100 kW/m².

It is more likely that a wave energy device will be driven by waves withperiods ranging from 10 to 7 seconds. With respect to this range of waveperiods, the maximum amount of power that can be made available forextraction within the throat of an optimized venturi device will rangefrom 147 to 210 kW/m², respectively.

A wave energy device with the same overall size, and differing only inthe cross-sectional area of its throat and embedded turbine (if any),can generate substantially more power when driven by waves of shorterperiods.

5b7. Two Examples of an Optimal Venturi Throat

FIGS. 11 and 12 show the relationship between the diameters of theventuri throat (relative to the diameter of the venturi mouth) for twosets of conditions that might exemplify the operation of submergedventuri devices.

FIG. 11 shows how the amount of power which would be available withinthe throat of a submerged venturi device, relative to the amount ofpower available at the mouth of the venturi, would change as aconsequence of the diameter of the venturi tube's throat (or thecorresponding cross-sectional area of the venturi device's throat) whenthe corresponding wave energy device were driven by waves with a heightof 4 meters and a period of 8 seconds, and the water were characterizedby a choke speed of 25 m/s (i.e. corresponding to a depth of about 22meters).

The relative amount of power available for extraction reaches a peak, ofabout 280 times the amount available at the mouth of the venturi device,(i.e. an absolute amount of 184 kW/m² in the throat compared to 0.7kW/m² at the mouth) when the diameter of the venturi throat is about 23%(i.e. 0.23) the diameter of the venturi tube's mouth. Under theseconditions, any other throat diameter, relative to the mouth diameter,will result in a sub-optimal amount of power being available.

The relative throat diameter corresponding to the optimal amount ofpower available for extraction is slightly less than the throat diameterat which the water's speed first begins to exceed the water's chokespeed. I.e. the optimal amount of power is found at a relative throatdiameter that is smaller than the diameter at which the water's chokespeed begins to limit the flow of water through the venturi tube.

FIG. 12 shows how the amount of power which would be available withinthe throat of a submerged venturi device would change as a consequenceof the diameter of the venturi tube's throat when the corresponding waveenergy device were driven by waves with a height of 6 meters and aperiod of 7 seconds, and the water were characterized by a choke speedof 30 m/s (i.e. corresponding to a depth of about 40 meters).

The relative amount of power available for extraction (per square meterof the cross-sectional area of the mouth) reaches a peak, of about 136times the amount available at the mouth of the venturi device, (i.e. anabsolute amount of 455 kW/m² in the throat compared to 3.3 kW/m² at themouth) when the diameter of the venturi throat is about 27.5% (i.e.0.275) the diameter of the venturi tube's mouth. Under these conditions,any other throat diameter, relative to the mouth diameter, will resultin a sub-optimal amount of power being available.

5b8. Calculate the Power for a Specific Throat Diameter

5b5a. Ambient Water Speed

For the purposes of this discussion, we will calculate the amount ofpower which will be available within a venturi device having arbitrarymouth and throat cross-sectional areas for waves with a constant heightof 4 meters, and a constant period of 8 seconds. We will further assumea depth of about 22 meters, and a corresponding choice speed of 25 m/s.We make our calculations relative to a venturi tube with a mouthpossessing a diameter of 5 meters, and a throat possessing a diameter of1.15 meters. (This corresponds to a venturi factor of 18.9.)

As a first step in calculating the power available for extraction withinthe throat of our sample venturi device, consider the characteristics ofthe wave that drives the vertical oscillations of the buoy and itsattached submerged venturi device.

Please refer to FIG. 13A. This figure illustrates the changes in theheight of the water's surface, as a function of time, whichcharacterizes the passing of a 4-meter wave.

FIG. 13B illustrates the vertical speed with which the height of theocean changes as a 4-meter wave passes. This is the same vertical speedthat will characterize the oscillations of the submerged venturi device.It will also define the speed at which water will enter the mouth of thesubmerged venturi device. (Note: Water will enter the upper mouth of thesubmerged venturi device as the wave carries the buoy, and submergedventuri device, higher. Water will then enter the lower mouth as thewave allows the buoy, and submerged venturi device, to fall.)

Note in FIG. 13B that the points of maximum vertical speed areassociated with the midpoints of the wave's height. The vertical speedfalls to zero at the peaks and troughs of such a wave.

5b5b. Calculate the Venturi Factor

The next step in calculating the power for a specific venturi throatdiameter (or for a specific venturi throat cross-sectional area) is todetermine the venturi factor for the venturi device (i.e. the degree towhich the speed of the water entering the venturi device's mouth will beamplified as it passes through the venturi device's throat).

In order to calculate the venturi factor for a particular venturidevice, we need to know the specific venturi tube mouth and throatdiameters (or equivalent specific venturi tube mouth and throatcross-sectional areas). In this example, the relevant diameters are:

Dm=venturi tube mouth diameter, e.g. 5 m

Dt=venturi tube throat diameter, e.g. 1.15 m

If the venturi device is not a radially symmetrical tube, then we canspecify the cross-sectional areas of the mouth and throat directly.However, if the device is a tube (as in this example), then we cancalculate the cross-sectional areas mathematically from the specifieddiameters:

Am=venturi tube mouth cross-sectional area

-   -   At=venturi tube throat cross-sectional area        Am=ΠDm ²/4=0.25Π(5 m)²        At=ΠDt ²/4=0.25Π(1.15 m)²

The venturi factor, “Vf” is defined as the ratio of the cross-sectionalareas of the mouth and throat. For this example, the venturi factor iscalculated as follows:Vf=Am/At=0.25Π(5 m)²/0.25Π(1.15 m)²=18.9

5b8c. Speed Through the Venturi Throat

FIG. 13C illustrates the speed profile (i.e. “amplified speed”) thatwould result from a simple multiplying of the speed of the waterentering the venturi device by the venturi factor. In other words, FIG.13C illustrates the result of amplifying, by the venturi factor, the“vertical speed of the wave surface”, i.e. the speed of the waterentering the mouth of the venturi device. This amplified speed profileis a simple amplification of the speed profile of the water entering theventuri device.

However, the actual speed of the water passing through the throat of theventuri device is limited by the choke speed of the water, i.e. 25 m/sin the case of this sample calculation. In FIG. 13C, the line entitled“choked amplified speed” illustrates what the profile of the speed ofthe water flowing through the throat of the venturi device wouldactually look like. Note that the speed does not exceed the choke speed.

5b8d. Power Available for Extraction Within the Venturi Throat

At any particular time on the x-axis of the graph in FIG. 13C, the speedof the water flowing through the throat of the venturi device can bedetermined. That speed is then used as input to the following equationto determine the power available for extraction at that particularmoment:

-   -   Vn=speed of the water flowing through venturi throat at time=n        seconds    -   Pn=power available for extraction in the venturi throat at        time=n seconds    -   Pn (Watts)=0.5 ρ At Vn³    -   ρ (seawater)=1025 kg/m³    -   At=0.25 Π(1.15 m)²=1.04 m²    -   V₂=25 m/s (determined through an examination of FIG. 13C)

Therefore, at the 2-second mark of the graph in FIG. 13C, where thespeed of the water flowing through the venturi throat is limited to thechoke speed of 25 m/s, the power available for extraction by a turbinewith a cross-sectional area equal to the cross-sectional area of theventuri throat will be:P ₂=0.5 (1025 kg/m³) (1.04 m²) (25 m/s)³=8,328,125 W=8.33 MW

At the 2-second mark, FIG. 13D indicates that the power available forextraction from the water flowing through the venturi throat (assuming aventuri factor of 18.9, as in this example) will be 424 kW/m² (i.e. 424kW per square meter of the mouth area of the venturi device). We canverify the agreement of our calculated result with the value indicatedin FIG. 13D:P ₂[chart]=(424 kW/m²) Am=(424 kW/m²) (0.25Π(5 m)²)=8.33 MW

5b8e. Average Power

After calculating the instantaneous power available for extraction withrespect to a multitude of evenly spaced moments during the period of thewave driving the wave energy device, the average power can becalculated.

The average amount of power associated with the power curve displayed inFIG. 13D is 234 kW/m². When multiplied by the cross-sectional area ofthe mouth of the venturi device considered in our example (i.e. by “Am”)this average power level equals 4.6 MW.

5b9. Calculate the Optimal Throat Diameter

The calculations illustrated above, for determining the power availablefor extraction with respect to a specific venturi throat diameter (orcross-sectional area) can be repeated for every throat diameter underconsideration, typically ranging from the diameter of the venturi mouthdown to 0 (exclusive of 0 of course).

FIG. 14 shows a graph created by evaluating the power available forextraction with respect to every possible relative throat diameterwithin the range of 1.0 (i.e. a throat with the same diameter as themouth) down to 0.0, exclusive (i.e. we don't actually evaluate arelative throat diameter of zero since this would preclude the flow ofany water). Repeating the calculation demonstrated above with respect toeach possible relative throat diameter creates the graph in FIG. 14.However, in FIG. 14 we used a mouth diameter of 1.0, and thecorresponding throat diameters are expressed relative to that unitymouth diameter.

We use relative throat diameters in FIG. 14 instead of actual diameterssince this is a more general illustration of the process. We couldtransform the graph in FIG. 14, in to an equivalent graph of the venturitube discussed in the example above simply by changing the scale of thehorizontal axis from its current 1.0-to-0.0, to an equivalent 5m-to-0.0. We would then adjust the vertical scale of each line in thegraph to correspond to the values that would be obtained from a venturidevice with a mouth diameter of 5 meters, instead of the 1-meter mouthdiameter used in FIG. 14. We could do this by multiplying the range ofvalues along the vertical scale in FIG. 14 by Am (as defined above).

The optimal relative throat diameter in FIG. 14 is found at 0.23,whereas the optimal specific (i.e. “non-relative”) throat diameter thatwould be obtained for the venturi device specified in our example abovewould be found at:Optimal throat diameter (i.e. optimal Dt)=0.23*Dm=0.23*5 m=1.15 m

5c. Optimization of Venturi Effect for a Variety of Waves

Locations where wave energy devices might be deployed are not generallycharacterized by waves of constant height and period. Any body of waterthat is perturbed by wind blowing across its surface will be populatedby waves of varying heights and periods. Therefore, any effort tooptimize the cross-sectional area of the throat of a wave energydevice's venturi tube will be improved by a consideration of what impactthe final design will have on the performance of the device with respectto the full complement of the various wave types which will drive it.

FIG. 15 shows a sample venturi-throat optimization with respect to fourdifferent wave types. The four lines in FIG. 15 correspond to waves ofheight: 2,4, 6 and 8 meters; and periods of: 7, 8, 9 and 10 seconds,respectively. Note that the optimal relative diameter (or correspondingrelative cross-sectional area) for the throat of a venturi device willbe different with respect to each of the four types of waves.

There are many ways to achieve a comprehensive optimization of thecross-sectional area of the throat of a venturi device. We will discusstwo of these ways below, with respect to the four sample wave typesspecified in FIG. 15.

5c1. Optimize Total Annual Energy Production

If you can determine the relative contribution of each wave type to thefull spectrum of wave types that will characterize a particulardeployment site (likely with respect to an annual survey), then you cancalculate, in the manner illustrated in FIG. 15, the optimal venturithroat diameter appropriate to each one. Then, by summing weightedcontributions of the available power associated with each of theparticular wave types evaluated, you can determine what the averageavailable power would be, over the time span represented by the survey,with respect to each venturi throat diameter evaluated, for a devicedeployed at such a site. In this manner, you can deploy a venturi devicethat possesses a venturi throat diameter that will result in an optimaltotal annual amount of power.

FIG. 16 shows two lines created through the summation of weightedcontributions from the four individual wave-type lines illustrated inFIG. 15. The two lines in FIG. 16 correspond to two different weightedsummations of the four lines of FIG. 15. One line in FIG. 16 correspondsto a representative “calm ocean” scenario in which the total wavecomplement contains contributions of 60% from 2-meter waves; 30% from4-meter waves; 8% from 6-meter waves; and 2% from 8-meter waves. Theother line in FIG. 16 corresponds to a representative “active ocean”scenario in which the total wave complement contains contributions of10% from 2-meter waves; 20% from 4-meter waves; 60% from 6-meter waves;and 10% from 8-meter waves.

FIG. 16 shows that with respect to the calm ocean wave profile theoptimal venturi throat diameter will be 0.185 (relative to the venturimouth diameter). And, with respect to the active ocean wave profile theoptimal relative venturi throat diameter will be 0.25.

If a deployment site were to be characterized by 7 months of relativelycalm oceans, as illustrated in the first line of FIG. 16 (e.g. perhapsduring the late spring, summer and early fall); and by 5 months ofrelatively active oceans, as illustrated in the second line of FIG. 16,(e.g. perhaps during the winter); then the optimal relative venturithroat diameter, as illustrated in FIG. 17, would be 0.23.

5c2. Optimize for Greatest Minimum Energy Production

If one desires to ensure that the contribution of electrical power froma farm of venturi-based wave energy devices is always at, or above, apredictable minimum level during any desired period of time, e.g. duringa typical year, with respect to particular intervals within that periodof time, e.g. with respect to every day, month, etc. during a typicalyear, then one can do the following:

-   -   1. Calculate the amount of power available with respect to every        throat diameter under consideration, with respect to the wave        complement characteristic of every interval during the specified        period of time (e.g. every month of a typical year).    -   2. Identify (e.g. plot) the minimum amount of power associated        with each of the specific intervals (e.g. each typical month)        with respect to each throat diameter.    -   3. And, identify the maximum power level in this set of        throat-diameter-specific minimum power levels. The throat        diameter associated with this peak minimum power level will keep        the overall power level of the farm of devices at, or above, the        greatest possible level over the desired period of time.

For example, with respect to the two wave scenarios evaluated in FIG.16, the optimal amount of power available during a “calm ocean” is lowerthan the amount available during an “active ocean”, therefore, theoptimal minimum relative venturi throat diameter needed to ensure thegreatest possible minimum level of power available within an optimizedwave energy device would be 0.185. This constitutes the relative throatdiameter which ensures that the amount of energy available within eachwave energy device during the periods of relatively “calm” (andrelatively “feeble”) oceans is maximized.

5c3. Greater Actual Complexity

Of course, the actual determination of an optimal venturi throatdiameter (or equivalent cross-sectional area) will be more complicatedthan suggested by the examples provided above. An actual determinationof the optimal diameter will likely involve a consideration of a broadrange, and high-resolution differentiation, of wave heights and periods.An optimization of a venturi device's relative throat diameter wouldlikely best be accomplished through the evaluation of one or more annualtabulations of high-resolution wave data characteristics observed at aprospective deployment site.

5d. Iterative Optimization

The methods of optimization described above are limited in manyrespects:

First of all, surveys of past wave characteristics may not be completelyaccurate. Such surveys sometimes represent hourly, or even daily, peak(i.e. most typical) wave heights and periods. In any case, it wouldlikely not be practical to log the height and period of every singlewave encountered at a site for an entire year. For this reason, theavailable historical wave data will almost always represent an imperfectestimation of the actual conditions.

Furthermore, even if a perfectly accurate high-resolution record couldbe obtained for a potential deployment site, it would always representan historical record of wave conditions. Such an historical record wouldlikely not provide a perfectly accurate prediction of future waveconditions.

Also, when multiple waves pass a point on the surface of the ocean inclose proximity to one another they “interfere” with one another. Inother words, a composite wave appears to pass such a point instead ofmultiple individual waves. This composite wave will be composed ofcontributions from each of the individual discrete waves involved, andit will likely lack a perfectly sinusoidal wave shape. The optimizationmethods discussed earlier were based on an assumption of purelysinusoidal waves.

In addition, the drag that a submerged venturi device will impose on thevertical movements of the associated wave energy device would beexpected to change, perhaps abruptly, when the water flowing through theventuri throat would, if it were able to do so, exceed the choke speedof the ambient water. When the speed of the water entering the venturidevice, after amplification by the venturi's characteristic venturifactor, would exceed the water's choke speed, then some of the waterwhich would otherwise enter the venturi device and flow through it, mustinstead be pushed out of the way by the rising or falling venturidevice. At such moments the drag imposed by the venturi device willincrease and the venturi device will begin to act like a parachute orsea anchor.

Such a pattern of irregular or non-uniform drag will tend to alter therate, phase and amplitude of a wave energy device's rising andfalling—causing it to deviate from a purely sinusoidal pattern. Theresulting irregular rate of vertical ascent and descent, as well as thereduced amplitude of the device's vertical motions, will violate theassumptions on which the prior discussions regarding the optimization ofthe venturi throat's diameter were based.

For all of these reasons, and others, the following would likelyconstitute a better optimization protocol:

-   -   1. Create an initial optimization of the relative venturi throat        diameter by a method similar to the ones discussed above. (If        the relationship between the drag of a wave energy device's        venturi and its speed can be determined through simulation, or        field trials, then this dynamic contribution to the vertical        speed of the device's venturi can be factored in to the        optimization methods discussed earlier.)    -   2. Deploy an initial device, perhaps a small prototype,        optimized by the method in step 1 above, at the selected site.    -   3. Monitor the actual speeds with which water enters the venturi        device (from either mouth) for a period of time (probably for        one year). This would likely best be accomplished by populating        a high-resolution array of water speeds with the average water        speeds encountered during fractional periods of time of a        constant duration (e.g. the average water speed detected during        every millisecond). If the goal of optimization is to maximize        the minimum energy available during any block of time of a        particular duration, e.g. during any particular 24-hour period,        then separate arrays could be utilized for every such block of        time, e.g. for every 24-hour period, in order to allow for the        optimization of the minimum power output.    -   4. a) To optimize for greatest annual total power output,        calculate the optimal venturi throat diameter on the basis of        this high-resolution array of water speeds in a manner similar        to the ones already discussed above.        -   b) To optimize with respect to maximizing the minimum energy            which will be made available during any block of time of a            specified duration, calculate the optimal venturi throat            diameter with respect to the speed-readings gathered with            respect to every such block of time, and use the throat            diameter associated with the greatest minimum power-level            threshold over all of the evaluated blocks of time.

An optimized throat diameter identified in this manner, if it differsfrom the throat diameter of the monitored device, will cause the deviceto encounter choke speeds at different times, and for differentdurations, than the monitored device when exposed to identical waveconditions (unless choke speeds are encountered by neither the monitorednor the optimized device). Therefore, although a single iteration ofthis procedure will likely result in a sufficiently optimized result, itmay be desirable to iterate this procedure multiple times, applying theoptimized throat diameter identified at the conclusion of each iterationto the device to be monitored during each subsequent iteration.

5e. Avoiding, or Reducing, Cavitation

When the water flowing through a venturi device is accelerated to apoint at which it reaches, and would, if possible, exceed, the chokespeed of the water, then cavitation will occur. (It will actually occurat the point at which the lateral pressure remaining in the water dropsbelow the vapor pressure of the water. And, the vapor pressure of thewater is dependent on the temperature of the water. Cavitation usuallyoccurs at a speed equal to, or only slightly greater than, the actualchoke speed.)

The relative venturi throat diameter (or equivalent relativecross-sectional area) at which the optimal amount of power is madeavailable for extraction with respect to waves of a particular heightand period, is often only slightly more narrow (i.e. associated withonly a slightly greater venturi factor) than the diameter at which thewater first begins to reach, or exceed, its choke speed. It may bedesirable in some circumstances, especially in cases where the materialsand/or design of a venturi device would render it especially susceptibleto damage from cavitation, to select a venturi throat diameter which,with respect to a given pattern of wave heights and periods, is slightlysub-optimal with respect to the amount of power generated, but whichnonetheless minimizes the likelihood that cavitation will occur.

Cavitation can sometimes (depending on the design and materials used)cause pitting, and in other ways damage, the components of a submergedturbine, and the walls of the venturi device, especially when suchcavitation occurs in close proximity to those components.

5f. Avoiding Ice Deposits

When the water flowing through a venturi device is accelerated, both itspressure and its temperature drop. If the temperature of the water dropsto, or below, the freezing point of that water then icing can occur. Ifthis problem is anticipated, or observed, then it may be desirable toreduce the venturi factor by utilizing venturi devices possessingrelatively larger throat cross-sectional areas than would be consideredoptimal solely in relation to the power output of those devices.

5g. Comparison of Preferred Embodiment with Similarly Sized Fleck Device

The optimized embodiments of venturi-based wave energy devices proposedhere, will generate significantly more power than similarly sized Heckventuri-based wave energy devices. Below we compare a Heck wave energydevice with a similarly sized device that has been optimized accordingto the method of this patent.

Let us assume the following conditions:

-   -   Wave height=4 meters    -   Wave period=8 seconds    -   Choke speed=25 m/s    -   Venturi mouth diameter=7 meters    -   Turbine efficiency=0.5

The diameter of the venturi throat of a Heck device, relative to theventuri mouth diameter, is 0.862 (as explained earlier).

The diameter of the venturi throat, relative to the venturi mouthdiameter, when optimized according to the method of this patent,relative to a wave height of 4 meters, a wave period of 8 seconds and achoke speed of 25 m/s is 0.23 (see FIG. 14).

Therefore:

Diameter of venturi throat:

-   -   For Heck device=0.862*7 meters=6.0 meters    -   For optimized device=0.23*7 meters=1.6 meters    -   For “No venturi”=1.0*7 meters=7.0 meters

Cross-sectional area of venturi throat:

-   -   For Heck device=Π*(6.0 m)²/4=28.3 m²    -   For optimized device=Π*(1.6 m)²/4=2.01 m²

Cross-sectional area of venturi mouth:

-   -   For all devices=Π*(7 m)²/4=38.5 m²

Venturi factor for device:

-   -   For Heck device=38.5 m²/28.3 m²=1.36    -   For optimized device=38.5 m²/2.01 m²=19.2    -   For no venturi, i.e. just an open turbine=1.0

As defined earlier, power available for extraction=0.5 A v³

Average available power for each device, with respect to water enteringthe mouth of the device with a speed profile as defined in FIG. 13B, andremembering the equation above:

-   -   For Heck device=60 kW    -   For optimized device=9,000 kW=9.0 MW    -   For no venturi=32.3 kW

As defined earlier, power actually extracted=0.5 k A v³

For the Heck device, the optimized device, and for an open turbinelacking a venturi device, the average extracted power equals k, or, inthis example 0.5, times the average available power.

While the Heck venturi device increases the amount of power extracted bythe device's turbine by less than 2×, a properly optimized venturidevice (the object of this invention) increases the amount of powerextracted by the device's turbine by 280×.

An optimized venturi-based wave energy device can generate 4,500 kW ofelectrical power while a similarly sized Heck device, driven by the samewaves, can only generate 30 kW. Or, in other words, a Heck device canonly generate 0.7% as much power as an optimized device when driven bywaves of the type specified in this example.

FIG. 18 shows a table summarizing this comparison of the Heck andoptimized wave energy devices.

FIG. 19 shows the differences in the amounts of power available forextraction within a Heck wave energy device, and a similarly sizedoptimized device. The optimized device provides significantly more powerwith respect to all wave heights. (For the sake of scale, only powerlevels corresponding to wave heights greater than, or equal to, 0.1meter are shown in FIG. 19.) Though not shown in FIG. 19, the optimizeddevice provides 2.4×109% more power at a wave height of 0.01 meter;61,500% more at a wave height of 2 meters; 15,400% more at a wave heightof 4 meters; and so on.

6. Alternate Embodiments

6a. All Optimal Submerged Venturi Devices

The scope of this invention is intended to cover all wave energy devicesemploying submerged venturi devices which incorporate a venturi effectwhich approaches, to any non-trivial extent, an optimal level withrespect to its real or anticipated pattern of movement in relation toits surrounding water; or, equivalently, all submerged venturi deviceswhich incorporate a venturi effect which approaches, to any non-trivialextent, an optimal level with respect to the pattern with which watermoves through the venturi device.

The difference between what is trivial and what is non-trivial withrespect to a venturi effect is necessarily subjective. However, aventuri factor of 2× appears to establish a reasonable threshold.Therefore, the scope of this patent is intended to include ant submergedventuri device that amplifies the speed of the water entering it by afactor that equals, or exceeds, 2×. Or, in other words, the scope ofthis patent is intended to include all submerged venturi devices whichdouble, or more than double, the speed of the water that enters thedevice.

With respect to this definition, the wave energy device proposed by Heckwould be regarded as incorporating a venturi effect of trivial extent,and Heck's device would therefore not infringe on this patent.

6b. All Types of Venturi Devices

The scope of this invention is intended to cover wave energy devicesemploying all types of submerged venturi devices when they are optimizedto any non-trivial extent. A venturi tube is the most obvious type ofventuri device. However, the scope of this invention also applies withequal force to non-trivially optimized venturi devices of other designs.For instance, the scope of this patent would apply to the venturi deviceembodiments illustrated in FIGS. 20 through 24, if they were optimizedto a non-trivial extent with respect to the degree to which they amplifythe speed of the water that enters their mouths.

6c. All Manner of Flotation Devices

The scope of this invention is intended to cover all wave energy devicesemploying submerged venturi devices that are moved partially, orentirely, by means of a loosely or rigidly attached flotation device.These flotation devices include buoys, boats, ships, and other objectsor devices which remain near, at, or above the surface of the water bymeans of their natural buoyancy, or by active means involving theexpenditure of energy, or by any other means.

6d. All Manner of Power Extraction

The scope of this invention is intended to cover wave energy devicesemploying venturi devices used in association with all manner of powerextraction devices and designs. For instance, the embodiments discussedat length in this patent involve venturi devices in which turbines arelocated in the throats of the venturi devices. The turbines are drivenby water flowing through the venturi devices. However, because they arepositioned in the venturi throats, the turbines are driven by the waterat the point of its greatest speed, and therefore at the point at whichthe water's kinetic energy, and associated extractable power, are attheir greatest.

While it would seem obvious that an optimal venturi design would place aturbine, or other power extraction component, in the narrowest portionof the venturi device (i.e. in the venturi throat), it is conceivablethat the power extraction could be accomplished at a location betweenthe throat and one or both mouths of a venturi device. The scope of thispatent is intended to cover all of these types of embodiments as well.

The scope of this invention is intended to cover not only wave energydevices employing venturi devices that incorporate a turbine in theventuri, but also those that utilize any, and all, other means ofutilizing the accelerated waters flowing through a venturi device toextract power.

One such alternate method of extracting power from the water flowingthrough a submerged venturi device is by means of exploiting thereduced, or absent, lateral pressure in the water whose speed isamplified by the venturi device. The scope of this invention is intendedto apply with equal force to wave energy devices that exploit the“suction” created by the water speeding through a submerged venturidevice, FIG. 23 illustrates one possible embodiment of this type ofventuri device power extraction scheme. The inlet of an air turbine isconnected to the atmosphere above the surface of the ocean. The exhaustfrom the air turbine, i.e. the port through which air is evacuated fromthe turbine, is connected to tubes that extend below the surface of theocean and into the venturi device. Holes positioned about the throat ofthe venturi tube allow air from the connected tubes to be drawn from thetubes and into the water flowing through the venturi throat.

As water flows through, and accelerates through, the venturi device, airis drawn out of the pipes connected to the venturi throat's suctionports. The suction induced in the pipes is communicated to the airturbine. And air is subsequently drawn out of one port in the turbine,and flows in from the other port. The flow of air through the turbinepowers the turbine. And the turbine's rotations can be used to drive agenerator or alternator.

This “air sucking” embodiment offers the advantage of allowing theturbine to be located in, or near, the buoy at the surface, thusfacilitating maintenance. It is likely that one-way valves would berequired in the air suction pipes to prevent the back flow of water into the pipes during the cyclic pauses in the suction which would beassociated with the peaks and troughs of the waves driving the submergedventuri's motion.

Other embodiments of such suction-based power extraction schemes arepossible, and these other embodiments would also be covered by the scopeof this patent.

Another alternate method of extracting power from the water flowingthrough a submerged venturi device is by a means similar to thesuction-based method described above. Instead of using the reduced, orabsent, lateral pressure of the water in the venturi throat to draw airthrough an air turbine, in this embodiment, the reduced, or absent,lateral pressure of the water in the venturi throat is used to drawwater through an external water turbine. FIG. 24 illustrates onepossible embodiment of this type of venturi device power extractionscheme. As with the air sucking embodiment, this “water sucking”embodiment also offers the advantage of allowing the turbine to belocated in, or near, the buoy at the surface. This would be expected tofacilitate any repair or maintenance activities.

Furthermore, during those recurring moments when the vertical motion ofthe buoy, and its attached submerged venturi device, pause betweencrests and troughs, the water in the suction tubes will be ready to beimmediately drawn out again once the vertical motion, and the associatedsuction, resume. With an air-based suction system like the one describedabove, water would tend to flow up from the venturi throat in to thesuction tubes during those moments when the suction pauses. With anair-based suction system it would likely be desirable to employ one-wayvalves, or some other mechanism, to prevent water from flowing in to thesuction tubes when the partial, or full vacuum, drawing the air out ofthe tubes was lost. If water were allowed to flow in to the suctiontubes between vertical movements, then some residual suction would belost, and power would be wasted. A water-based suction power extractionmethod would not necessarily require such one-way valves. Also, becausewater is largely incompressible, a water-based suction scheme wouldlikely have a higher efficiency than an air-based scheme.

The scope of this patent is intended to apply with equal force to waveenergy devices that utilize any kind of power extraction and generationscheme, and regardless of whether or not power extraction occurs within,or outside, the throat of the venturi tube. In particular, the scope ofthis invention is intended to apply to wave energy devices utilizinggenerators, alternators, or any other means of converting mechanicalenergy into electrical energy. The scope of this invention is alsointended to apply to wave energy devices utilizing any other means ofconverting the energy obtained from the ocean by such devices in to anyother form of useful energy, e.g. converting such energy in to usefulforms of chemical energy. The scope of this invention is also intendedto apply to wave energy devices utilizing the energy made availablewithin, or outside, the throat of an optimized venturi device toaccomplish any useful function, e.g. to desalinate seawater, to extractminerals from the ocean, to capture and sequester carbon in the ocean orthe atmosphere, etc.

6e. All Manner of Venturi Movement

The scope of this invention is intended to cover wave energy devicesemploying venturi devices that are moved vertically, or horizontally, inresponse to wave motion near the surface of the ocean. However, it isalso intended to cover those energy devices, which operate on the ocean,or on other large bodies of water, and which employ venturi devices thatare lifted partially, substantially, or entirely, by other means. Forinstance, the scope of this patent is intended to apply to those waveenergy devices that move their attached submerged venturi devicesentirely by means of the wave-induced motions of their attachedflotation devices. It is also intended to apply to those wave energydevices that supplement the movement of their attached venturi devicesby means of mechanical devices, hydraulic devices, winches, compressedair, etc. There may be some advantage to be gained by using such activemeans to partially, or fully, move a submerged venturi device relativeto the supporting flotation device. For instance, it may be desirable touse such secondary lifting means to partially oppose the naturalvertical motion of the waves. The purpose of this artificial countermotion might be to change a primarily sinusoidally varying verticalmotion into a more linear motion. This could allow the venturi device toutilize a greater venturi factor, and to enjoy waters traveling at themaximum rated venturi throat speed for longer periods of time, whileperhaps also avoiding the increases in drag and turbulence which wouldbe associated with non-linear water speeds which would not just reach,but would, if possible, exceed the choke speed of the device, thusfurther maximizing the extraction of power from such wave-inducedvertical motion. The purpose of such active movements of a submergedventuri device might also be to increase the amplitude of the submergedventuri device over that which would be provided naturally by thedriving waves.

FIGS. 25A and 25B illustrate another embodiment of this invention. Thisembodiment incorporates two optional features either of which, or bothof which, may be incorporated in an embodiment of this invention.

In the embodiment illustrated in FIGS. 25A and 25B, the struts 227, orcables, which at one end are attached not directly to the buoy 26, butinstead to a platform 81. The platform 81 is then attached to one ormore lifting means 80 a and 80 b. These lifting means, are then attachedto the buoy 26. Thus, the lifting means are able to modify the degree towhich the buoy and venturi tube are vertically separated. These liftingmeans can be used to modify the vertical separation, and the verticalmotion of the submerged venturi tube so that its motion is no longerprecisely synchronized with that of the waves passing beneath the buoy.

In the absence of this lifting means, the vertical speed of thesubmerged venturi tube, and the speed with which water enters themouth(s) of the venturi tube, moves between maxima and minima in asinusoidal fashion. This means that the optimization of the venturitube's design by the method of this invention, must try to find anoptimal balance between these extremes of ambient water speed.

Through the incorporation and use of this lifting means, the verticalmotion of the submerged venturi tube is partially decoupled, by means ofactive lifting (or dropping) of the venturi tube with respect to thebuoy. Thus, the sinusoidal motion of the waves which drive the motion ofthe buoy can be used to generate a less extreme vertical movement of theattached venturi tube. Thus, the method of optimization described inthis invention can be applied to a “flatter” and more constant patternof water movement and speed. This will make it possible to incorporate arelatively narrower venturi throat, and to generate greater amounts ofpower, with respect to any particular wave pattern. Of course, it willalso add complexity and cost to this wave energy device, and wouldlikely increase the amount of maintenance required.

FIG. 25B also illustrates another optional feature of this invention. Inthis embodiment, the generator 46 is attached, not directly to the buoyas in the preferred embodiment, but to a platform 83. This platform 83is attached to one or more lifting means 82 a and 82 b. These liftingmeans are then attached directly to the buoy (not illustrated), or, asillustrated in FIG. 25B, to the platform 81 of the venturi tube liftingassembly. Thus, it becomes possible to move the position of thegenerator, and its attached shaft or cable, and the attached turbine,with respect to the venturi tube. This generator-lifting assembly makesit possible to move the turbine in to, and out of, the throat of theventuri tube to a certain extent.

Moving the turbine out of the throat of the venturi tube can be used toaccomplish a number of desirable objectives. For instance, when thewater in the narrowest portion of the throat of the venturi tube ismanifesting, or about to manifest, cavitation, then moving the turbineto a position in the venturi tube in which the water's speed is slower,and cavitation is absent, can help to prevent damage to the turbine, Itwould also be possible to create a more constant rate of angular motionin the turbine, shaft and generator, by incrementally moving the turbineaway from the throat as the speed of the water in the throat isaccelerating, and toward the throat as the speed of the water isdecelerating, it will be possible to expose the turbine to a moreconstant rate of water flow. This would in turn cause the attachedgenerator to be driven with a more uniform rate of turning.

Either the venturi tube lifting means, or the generator lifting means,or both, can be incorporated in to an embodiment of this invention toachieve desirable effects.

What is claimed is:
 1. A wave energy apparatus, comprising: a venturishroud which when the apparatus is in an operative position in a body ofwater is positioned in the body of water a distance below a surface ofthe water; the venturi shroud being positionable in an open position andan alternative closed position; the venturi shroud when in the openposition forming a venturi channel having a top mouth and a bottomconstricted region; and a turbine attached to the venturi shroud andpositioned so as to be powered, when the apparatus is in the operativeposition, by water accelerated by the venturi channel as the venturishroud moves due to wave action in the body of water.
 2. The apparatusof claim 1 wherein with the apparatus in the operative position, theventuri shroud is moved to the open position as the venturi shroud ismoved upwardly by wave action and the venturi shroud is moved to theclosed position as the venturi shroud is moved downwardly by waveaction.
 3. The apparatus of claim 1 wherein the venturi shroud includesa bottom cylindrical portion that forms at least a portion of theconstricted region and in which the turbine is disposed.
 4. Theapparatus of claim 1 wherein the venturi shroud has a top frusto-conicalportion and is free of any bottom frusto-conical portion.
 5. Theapparatus of claim 1 further comprising a flexible connection from whichthe venturi shroud hangs when the apparatus is in the operativeposition.
 6. The apparatus of claim 1 wherein the venturi shroudincludes pivotal ribs and flexible material connected to the ribs todefine the open position.
 7. The apparatus of claim 6 wherein theventuri shroud includes a cylindrical portion to which the ribs arepivotally attached and which forms at least a portion of the constrictedregion.
 8. A wave energy apparatus, comprising: a venturi shroud whichwhen the apparatus is in an operative position in a body of water ispositioned in the body of water a distance below a surface of the water;the venturi shroud being configured to form a venturi channel having atop mouth and a bottom constricted region; a turbine attached to theventuri shroud and positioned so as to be powered by water acceleratedby the venturi channel as the venturi shroud moves due to wave action inthe body of water when the apparatus is in the operative position; aflexible connection from which the venturi shroud hangs when theapparatus is in the operative position; and the venturi shroud having atop frusto-conical portion and being free of any bottom frusto-conicalportion.
 9. The apparatus of claim 8 further comprising a buoy, theflexible connection connecting the venturi shroud to the buoy.
 10. Theapparatus of claim 8 wherein the venturi shroud has a lower cylindricalportion attached to a bottom of the top frusto-conical portion, and thetop frusto-conical portion is longer than the cylindrical portion. 11.The apparatus of claim 8 further comprising a generator powered by theturbine, and the flexible connection including an electrical cord fromthe generator.
 12. The apparatus of claim 11 wherein the generator isdisposed in the venturi channel.
 13. The apparatus of claim 11 whereinthe generator is disposed entirely within the venturi shroud.
 14. A waveenergy apparatus, comprising: a venturi shroud which when the apparatusis in an operative position in a body of water is positioned in the bodyof water a distance below a surface of the body of water: the venturishroud being configured to form a venturi channel having a top mouth anda bottom constricted region; a turbine attached to the venturi shroudand positioned so as to be powered by water accelerated by the venturichannel as the venturi shroud rises due to wave action in the body ofwater when the apparatus is in the operative position; the venturishroud having an upper frusto-conical portion that includes the topmouth and a lower cylindrical portion that is defined by the bottomconstricted region; the venturi shroud being free of any bottomfrusto-conical portion below the lower cylindrical portion; and aflexible connection from which the venturi shroud hangs when theapparatus is in the operative position.
 15. The apparatus of claim 14wherein the flexible connection includes an electrical cable.
 16. Theapparatus of claim 14 wherein the venturi shroud is flexible andcollapsible.
 17. The apparatus of claim 14 wherein the venturl shroud isrigid and non-collapsible.
 18. The apparatus of claim 14 furthercomprising a rigid central portion to which the venturi shroud isattached, and a generator powered by the turbine and attached to therigid central portion.
 19. The apparatus of claim 14 wherein the venturishroud is positionable in an open position and an alternative closedposition due to the wave action.
 20. The apparatus of claim 19 furthercomprising an elongate storage canister in which the venturi shroud ispositionable when in the closed position but not in the open position.21. A wave energy apparatus, comprising: a venturi shroud which when theapparatus is in an operative position in a body of water is positionedin the body of water a distance below a surface of the body of water;the venturi shroud being configured to form a venturi channel having atop mouth and a bottom constricted region; a turbine attached to theventuri shroud and positioned so as to be powered by water acceleratedby the venturi channel as the venturi shroud rises due to wave action inthe body of water when the apparatus is in the operative position; thebottom constricted region being formed by a collar having a lower freeend and a constant cross-sectional area; the top mouth being anuppermost water passageway of the venturi channel and the collar being abottommost water passageway of the venturi channel; and a flexibleconnection from which the venturi shroud hangs when the apparatus is inthe operative position.
 22. The apparatus of claim 21 wherein the collaris a cylindrical collar.
 23. The apparatus of claim 21 wherein theturbine is positioned in the collar.
 24. The apparatus of claim 21wherein the venturi shroud is flexible and collapsible.
 25. Theapparatus of claim 21 wherein the venturi shroud is rigid andnon-collapsible.
 26. The apparatus of claim 21 wherein the venturishroud is positionable in an open position and an alternative closedposition due to the wave action.
 27. The apparatus of claim 26 furthercomprising an elongate storage canister in which the venturi shroud ispositionable when in the closed position but not in the open position.28. The apparatus of claim 21 further comprising a rigid central portionto which the venturi shroud is attached, and a generator powered by theturbine and attached to the rigid central portion.
 29. The apparatus ofclaim 28 wherein the generator includes an electrical cord, and theflexible connection includes the electrical cord.
 30. A wave energyapparatus, comprising: a venturi shroud which when the apparatus is inan operative position in a body of water is positioned in the body ofwater a distance below a surface of the water: the venturi shroud beingconfigured to form a venturi channel having a top mouth and a bottomconstricted region; a turbine attached to the venturi shroud andpositioned so as to be powered by water accelerated by the venturichannel as the venturi shroud moves due to wave action in the body ofwater when the apparatus is in the operative position; a flexibleconnection from which the venturi shroud hangs when the apparatus is inthe operative position; the venturi shroud narrowing from the top mouthto a bottom of the venturi shroud; the venturi shroud being positionablein an open position and an alternative closed position; and the venturishroud when in the open position forming the venturi channel having thetop mouth and the bottom constricted region.
 31. The apparatus of claim30 wherein the top mouth is the uppermost water passageway of theventuri channel and the bottom constricted region is the bottommostwater passageway of the venturi channel.
 32. The apparatus of claim 30wherein the bottom constricted region is formed by a collar having alower free end.
 33. The apparatus of claim 30 wherein the flexibleconnection includes an electrical cable.
 34. The apparatus of claim 30further comprising a buoy, the flexible connection connecting theventuri shroud to the buoy.
 35. The apparatus of claim 30 wherein theturbine is powered by accelerated water when the venturi shroud is inthe open position.
 36. The apparatus of claim 30 wherein with theapparatus in the operative position, the venturi shroud is moved to theopen position as the venturi shroud is moved upwardly by the wave actionand the venturi shroud is moved to the closed position as the venturishroud is moved downwardly by the wave action.
 37. The apparatus ofclaim 30 wherein the venturi shroud includes a bottom cylindricalportion that forms at least a portion of the constricted region and inwhich the turbine is disposed.
 38. The apparatus of claim 30 wherein theventuri shroud has an upper frusto-conical portion and is free of anybottom frusto-conical portion below the bottom constricted region. 39.The apparatus of claim 30 further comprising a buoy, and the flexibleconnection connecting the venturi shroud to the buoy.
 40. The apparatusof claim 30 further comprising a generator powered by the turbine, andthe flexible connection including an electrical cord from the generator.41. The apparatus of claim 30 further comprising a rigid central supportattached to the venturi shroud to provide orientation stability thereto.42. The apparatus of claim 30 wherein the venturi shroud when in theclosed position and not in the operative position is configured to fitin an elongate storage canister.
 43. The apparatus of claim 30 furthercomprising an elongate storage canister in which the venturi shroud ispositionable when in the closed position but not in the open position.44. The apparatus of claim 30 wherein the venturi shroud includespivotal ribs and flexible material connected to the ribs to define theopen position.
 45. The apparatus of claim 44 wherein the venturi shroudincludes a cylindrical portion to which the ribs are pivotally attachedand which forms at least a portion of the constricted region.
 46. Theapparatus of claim 30 further comprising a generator powered by theturbine, and the flexible connection including an electrical cord fromthe generator.
 47. The apparatus of claim 46 wherein the generator isdisposed in the venturi channel.
 48. The apparatus of claim 46 whereinthe generator is disposed entirely within the venturi shroud.
 49. Theapparatus of claim 30 wherein the venturi shroud has an upperfrusto-conical portion that includes the top mouth and a lowercylindrical portion that is defined by the bottom constricted region.50. The apparatus of claim 49 wherein the upper frusto-conical portionis longer than the lower cylindrical portion.
 51. The apparatus of claim49 wherein the turbine is disposed in the lower cylindrical portion, andfurther comprising a generator powered by the turbine and disposed inthe upper frusto-conical portion.
 52. A wave energy apparatus,comprising: a venturi shroud which when the apparatus is in an operativeposition in a body of water is positioned in the body of water adistance below a surface of the body of water; the venturi shroud beingconfigured to form a venturi channel having a top mouth and a bottomconstricted region; a turbine attached to the venturi shroud andpositioned in the bottom constricted region so as to be powered by wateraccelerated by the venturi channel as the venturi shroud moves upwardlydue to wave action in the body of water when the apparatus is in theoperative position; a rigid central portion to which the venturi shroudis attached; a generator powered by the turbine and attached to therigid central portion; a flexible electrical cable from the generator;the rigid central portion and the generator attached thereto hanging viaa flexible connection from a buoy, boat or ship floating in the body ofwater when the apparatus is in the operative position; and the flexibleelectrical cable being the flexible connection.
 53. The apparatus ofclaim 52 wherein the venturi shroud is positionable in an open positionand an alternative closed position due to the wave action.
 54. Theapparatus of claim 52 wherein the venturi shroud is flexible andcollapsible.
 55. The apparatus of claim 52 wherein the venturi shroud isrigid and non-collapsible.
 56. The apparatus of claim 52 wherein thegenerator is positioned in the venturi shroud.
 57. A wave energyapparatus, comprising: a venturi shroud which when the apparatus is inan operative position in a body of water is positioned in the body ofwater a distance below a surface of the body of water; the venturishroud being configured to form a venturi channel having a top mouth anda bottom constricted region; a turbine attached to the venturi shroudand positioned in the bottom constricted region so as to be powered bywater accelerated by the venturi channel as the venturi shroud movesupwardly due to wave action in the body of water when the apparatus isin the operative position; a rigid central portion to which the venturishroud is attached; a generator powered by the turbine and attached tothe rigid central portion; a flexible electrical cable from thegenerator; the rigid central portion and the generator attached theretohanging via a flexible connection from a buoy, boat or ship floating inthe body of water when the apparatus is in the operative position; andthe venturi shroud being positionable in an open position and analternative closed position due to the wave action.
 58. A wave energyapparatus, comprising: a venturi shroud which when the apparatus is inan operative position in a body of water is positioned in the body ofwater a distance below a surface of the body of water; the venturishroud being configured to form a venturi channel having a top mouth anda bottom constricted region; a turbine attached to the venturi shroudand positioned in the bottom constricted region so as to be powered bywater accelerated by the venturi channel as the venturi shroud movesupwardly due to wave action in the body of water when the apparatus isin the operative position; a rigid central portion to which the venturishroud is attached; a generator powered by the turbine and attached tothe rigid central portion; a flexible electrical cable from thegenerator; the rigid central portion and the generator attached hangingvia a flexible connection from a buoy, boat or ship floating in the bodyof water when the apparatus is in the operative position; and theventuri shroud being flexible and collapsible.
 59. An apparatus thatconverts wave energy to electrical energy, comprising: a buoy adapted tofloat on a water surface; a shroud having a first end and a second end;the first end adapted to open by water flow through the shroud in afirst direction; the shroud forming a conical shape when the first endis opened by water flow in the first direction; a rigid central supportdisposed in interconnecting relation between the buoy and the shroud; arigid collar at the second end of the shroud; a plurality of rigid framemembers having a first end pivotally connected to the rigid collar incircumferentially spaced relation to one another; the shroud adapted tointerconnect the rigid frame members to one another; a turbineconcentrically positioned within a space surrounded by the rigid collar;the turbine adapted to be connected to a generator; the shroud adaptedto funnel water toward the turbine when the first end of the shroud isheld open by the water flow in the first direction; and the rigid framemembers adapted to pivot toward the rigid central support by water flowthrough the shroud in a second direction opposite to the firstdirection.
 60. The apparatus of claim 59 wherein the shroud is flexibleand collapsible.